BV3 Thoughts and Suggestions

[Alsadius]

BV2 is a pretty decent system in most ways, but it's got a few obvious holes, especially around certain badly over-costed gunnery bonuses. I've mulled over suggestions for updating it for a while, so here's my thoughts.

First off, BV2 is about as complex as you can realistically get for pen-and-paper. If I'm complaining that it's not good enough on certain points, then realistically I'm saying that it needs to be more complex, and that means that I'm designing a system for computerized use. That means that this will almost certainly be an unofficial system that gets used by MegaMek or by unit creator programs, instead of being a part of the main rulebooks. But with that said:

Weapon Values
The current formula for most weapons is simple enough. Take the average damage a weapon would do at each range increment (assuming the usual range penalties and a 4-skill gunner, but no other penalties), add them all up, and then multiply by 1.2 if it's an energy weapon, or 1.5 if it isn't. Then add another 20% if it can one-shot a head (i.e., a 12-damage cluster or more). 

You also factor in heat, with the assumption that the mech is willing to go up to +6 on any given turn, and weapons above that are halved in value.

Note the assumptions and implications here:
- Every range is considered equally important, from up close to distant.
- Because ammo costs are equal to one-eighth of the weapon's cost, a ballistic/missile weapon with two tons of ammo is as expensive as an otherwise-identical energy weapon that doesn't actually need ammo in the first place. And energy weapons that need ammo (like the plasma rifle) are charged both the higher energy weapon rate plus ammo costs on top.
- Crit-seeking potential and flexibility (e.g., LBX autocannons) are not treated as being worth any increase in value. Weapons with range choices (like ATMs) seem to have a weird hybrid formula - an ATM6 would be worth 147 if it used its best ammo at every range, or 83-89 if you confined it to any single ammo type, but it's actually worth 105.
- The implied combat is a 4-skill gunner shooting a target that has no defensive bonuses at all. This is way too low a to-hit for most fights.
- Only Mechs are considered as possible targets.

Also, note some of the inconsistencies in how gunnery bonuses are treated:
- If you give a normal weapon(no min range, short/med/long all the same size) the pulse bonus of -2 to hit, then the math works out that weapon's cost goes up 28.3%.
- A targeting computer that gives -1 to-hit increases the BV of the linked weapons by 25%, so almost as much as a pulse's -2.
- If you give a gunner -2 gunnery skill, the total cost of the mech goes up 60%. (Since that includes BV other than the weapons themselves, this is going to be the equivalent of increasing the weapon BV by over 100% in most cases.)
- If you put a unit in a C3 network, the total BV of the unit goes up by 10-60% depending how big the network is. The best-case bonus of C3 is -4 to hit, but realistically I wouldn't value it much above -2.
- Physical attacks are priced in by adding the mech's tonnage, but this is dramatically more expensive than a comparable weapon would be. For a 100-tonner, the 20-point kick is worth 35 by the usual formula, but BV2 makes you pay 100 for it.

So, here's my suggestion.

1) Start with the same formula of each range being equally important.

2) Instead of using a simple value for each weapon that's calculated in advance, calculate it on the fly, for the mech as a whole. Factor in the pilot's gunnery skill, targeting computer, and so on, and also consider heat. At each possible range, figure out the maximum heat-efficient expected damage, the maximum alpha strike expected damage, and then take the average of the two. Sum the ranges all up, and that is your basic offensive BV. (Then multiply by a mobility factor, as usual). Physical attacks are just another weapon to be put into this calculation.

3) When doing the above calculation, assume a +3 to-hit mod, on top of weapon mods and the pilot's gunnery skill. This might still be a little low, but it's a lot closer to reality.

4) To deal with crit-seeker weapons, add +0.5 to the damage dealt by each cluster. A medium laser gets calculated as if it deals 5.5 damage, each SRM gets calculated like it's doing 2.5 damage, and so forth.

5) For ammo, ditch the separate cost for stored ammo, and instead judge it by shots per gun. One shot is worth 20% of what an equivalent unlimited-ammo weapon would be(which works out the same as the current 25% rule for one-shot missiles), and each shot brings it 20% closer(multiplicatively). This works out to about 90% of the BV if you have 10 shots per weapon, which is basically equal to one ton of ammo per weapon (so AC/10s are about the same, for example). Round shots per gun up.

6) For C3 networks, you adjust the range penalties on guns. Use math similar to the ammo design above - each other mech in the C3 network gives you a 20% better chance to avoid range penalties(multiplicatively), and when you calculate the BV of a weapon at a given range, you'd use a weighted average of a no-range-penalty weapon and the usual weapon.

Defensive Values
I have a lot fewer complaints about BV2 here, tbh. The only thing I can see to tweak is the penalty for exploding ammo/Gauss rifles in your mech.

For each slot, figure out the damage it would do if it got critted. Each damage reduces the defensive BV by 0.1(capped at the maximum amount it could inflict), and each section of the mech it'd destroy outright reduces the defensive BV by an additional 1. So a full load of LRM ammo in a side torso is 120 damage, and blowing that would kill the mech outright, so all 8 sections are up for destruction. 120*0.1 + 8*1 = 20 BV reduction. But if you put CASE on, it'd only be able to do damage equal to the HP of the side torso and arm(say 50), and only destroy two sections. 50*0.1 + 2*1 = 7 BV reduction from the same ammo with CASE.

There's obviously far more involved in setting up a true BV system than just the above - it doesn't count the ability to damage anything besides mechs/vehicles, it doesn't include a lot of TacOps and StratOps rules, the value of simply having an initiative sink, and so forth. But I think that's enough to start with, as a vision of where to take the next iteration of BV.

[DevianID]

Good stuff.  Starting from the bottom, the initiative sink issue--this is force building, which has a different balance from battle value.  If force building rules required both sides to have equal units, then as long as the battle value is fairly calculated it wont matter.  My issue is that a 17 battle value unit exists, but if that unit does nothing other then exist it really doesn't have a battle value, and if both sides are equal then one 17bv unit counters the other and no initiative sink issue exists.  I digress.

For me, weapon BV seems best balanced around 5 turns.  If it was 10, the value chosen in alpha strike, it could also work, but existing BV cost structures, like one shot weapons, are valued at 20%, so 5 turns is the value chosen by TPTB.  5 turns is also enough to really change the game state in normal btech played on 2 paper maps--games going for 30+ turns on 3x3 maps id argue are not ones we can ever find balance in, as the scope is too different from the core gameplay.  When you do your rolling 5 turn damage spread, heat is much better balanced, as is ammo.  Ammo past 5 shots per gun doesn't cost extra BV, to help the ammo versus energy discrepancy.  IE, the mech with 56 shots of gauss ammo for 2 guns isn't being forced to pay an arm and a leg for 46 of the 56 shots, like it is now.  Heat, instead of doing +6 per turn which is obviously not sustainable, is now +6 over 6 turns.  This provides the necessary difference units like the Spider 7m, with 16 heat generation and 10 dissipation, and the 8m, with 16 generation and 20 dissipation, deserve.  Currently they cost the same, which is obviously off.  Also, heat should be calculated as the best BV/heat, not the highest BV first.  Currently, the Rifleman pays for the 2 large lasers first, and the AC/5s are half cost.  In reality, the AC/5s are always fired first as they are more efficient per heat, then 1 large laser, and everything after that would be discounted.  Weapons on a grossly overheating mech that never get fired in a 5 turn rolling average should be discounted down to 20%, which represents that 1 in 5 turn alpha strike.  In the rifleman example, the AC/5s and 1 large laser pay full value, one medium laser will pay 40% value for firing 2 times (for the 6 floating heat the calculation allows), and the second large laser and medium laser will cost 20%, being weapons of last resort that never actually fire, but do provide some value to have in a pinch.  20% is plenty fair.

I agree with you, as pulse is undervalued, BUT... mathy stuff.  A PPC, stock standard, is 176.  That same weapon with -2 from a 'pulse' bonus would cost 233, 32% more.  If all weapons were calculated with +3 base to hits, the base of a PPC would be 72 (before adjustments) compared to 141 for a weapon with only +1 base to hit.  Thus, in your system using a +3 'guessed' TMM/whatever, pulse would DOUBLE, (+96% in this example), the cost of a weapon like a PPC.  On the table, this would mean 9s versus 7s (+110%), and 8s versus 6s (+73%) would be the 'break point' when pulses become better--i dont see many weapons landing at 9s in a normal game such that we need to penalize pulse.  This is probably too high, when for +40% for the whole mech, you can get -2 from a better gunnery in the system.  On something like a Battle Cobra, 1487, the pulse lasers will go from 265 (at +28% markup with pulse from 207 base) to 378 from a +83% increase.  The equal new mech would cost 1859 in your system if the weapons were normalized, versus ~1325 if the guns didnt have the pulse bonus.  At ~1325, a 40% increase from the whole mech would make it cost 1855--meaning pulse lasers in a system with a +3 TMM factored into the weapons would make pulse lasers more expensive then non pulse with the WHOLE MECH upgraded in gunnery skill. 

Thats a lot of math, but more or less it just shows that +3 calculated 'TMM', while it might seem was realistic and maybe too low, is actually too much and isnt good for balance.  The BV change in weapons it would make would mean that you would get really, really cheap long range bracket value with an effective discount, since the +3 would make the value added from, say, an ER PPC's long range of 15 to 23, worth nothing to buy (4 base, 4 range, +3 assumed tmm, means the value purchased from the 9 hexes at 15-23 would be 1/12th the damage, from the 3/36 chance your formula provides with that +3 bonus.  AKA, an ER PPC that stops at 14 would cost only 11.25 BV less.  Those 9 extra hexes costing only 11 BV is criminally cheap.  Id pay 11.5 BV to extend the long range of any gun in the game 9 hexes.  Yes, you might be shooting at +3 tmm some of the time, but not all of the time.  And when you arnt shooting at +3 tmm, your BV system means that long range weapons will turn anything to dust with less then a +3 bonus, as they get so many more long range weapons for the same BV.  Hyperbole, yes, im exagerating for effect.  But if you make them pay as if long range is an 11 to hit, and its actually less then that, the value goes from 1 in 12 up to 15/36 for no TMM, a 500% increase, from the long range BV you paid for.

[DevianID]

The +3 TMM thing aside, things like jump jets and MASC need adjustments.  They do have value, but not as much as the system charges them for.  Masc is quite simple, it should be calculated as being on 3 of the 5 turns in a 5 turn rolling average (instead every turn), and the little bit of damage done from 3 1-in-36 failure rolls should be subtracted from it's BV.  Same thing with jamming weapons--they should only cost 95%, as in 5 turns with a 1/36 jam chance, you will only get 95% of your total paid for 5 shots.  Jumping does increase your offense, but not by the amount paid for, as it also increases your to-hit mods by +1 more then running.  Thus, a 5/8 mech currently pays 1.37 as an offensive speed factor, which makes sense.  5/8/5, with its much larger hex threat range, pays 1.76 for the speed factor, BUT those shots are at +1 more penalty compared to running.  So, the speed factor of a jumping mech (equal to 13 hexes of offensive threat, 8 running +5 jump) should be less then a running mech with 13 hexes of threat (if such a mech existed), as a mech that can move 13 hexes with a run wont have the +1 jump penalty.  Thus, the jumping speed factor should be 82% per jump jet, the discount from being +1 harder to hit with.  A 5/8 to 5/8/5 should go from 8 hexes to 12 (not 13), as only 82% of the jump jets get counted.  With a speed factor of 12 hexes, a 5/8/5 should have a 1.63 BV modifier, instead of the 1.76 it pays now.

[Alsadius]

Fair point regarding force value versus unit BV - that's a whole additional layer, which even official BT has gone back and forth on, so I should probably leave it out of this discussion.

The five-turn rule isn't a bad rule of thumb, but I wouldn't hard-cap the related calculations or anything. I think we'd agree that three SRM6 with one ton of ammo is a less useful loadout than the same three SRM6 with two or three tons of ammo - even if five turns is the average length that a Mech will stay alive for once combat is properly joined, the nature of averages is that you go over about half the time. It can be a goal to balance around, though.

Regarding your pulse math...yeah, I think pulse is that good. Most attacks that matter for no-bonus weapons are rolled on to-hits of about 6-9 - if it's higher than that it's not doing much, and if it's lower than that you're probably just finishing off a cripple. A -2 bonus on a base to-hit of 9 is +110% expected damage. On 8, it adds 73%, on 7 it adds 43%, and on 6 it adds 27%. And if you're doing early-battle chipping away, it's even better - a pulse bonus on a base to-hit of 12 is +500% damage. (The relevance of these numbers change if you have a real pimp gunner, but of course the proposal would take that into account - if you have a 1-gunnery Mechwarrior, then the BV costs of the current system are replicated exactly for pulse bonuses.)

That said, if we want to add another layer of complication, maybe you'd look at the BV with +0, +1,...+5 mods, and average them out. That should address some of your concerns.

And yes, agreed regarding MASC/TSM. I'd probably just average out the "on" and "off" BVs, make the implicit assumption that they're used half the time. But making things simpler like that is just my default style (don't laugh - I might make the big picture ridicu-complicated, but I will use nice round numbers if I can possibly help it.)

[DevianID]

I do agree that 5 turns of ammo is rough, but 50 turns of ammo is too much.  I think alpha strike, at 10 turns, was best.  5 turns matches the existing BV cost for 1 shot weapons though, so I went for that since that's the current formula.  Also, its fair that every shot after 5 should be discounted more and more, as its less and less likely a mech is alive to shoot it.  Some exponential decay is the best bet, since a computer is calculating it.  Off the cuff, I'd say the average mech has a 75% chance of living to turn 10?  Id stop increasing the BV for ammo altogether at turn 13+.

For the 5 turn MASC rule, I like it as a simple 50% doesnt adequately describe how often you can use the system since you can MASC back to back, or on turns with no visible targets cool it down for no penalty.  So 3 times in 5 turns felt better then 100% (current) and 50% (the often quoted number).

As for pulse, I see why you think its that good at the top end of the bell curve.  But what about the whole point of my math, which shows that pulse in your pricing makes a unit so expensive it can just buy -2 gunnery for the whole mech, instead of pulse on 2 guns, and be CHEAPER, using standard weapons with 2 gunnery instead of pulse. 

This is where deciding on a turn limit can help.  In a "play till you die" game with enough maps, then the upper end of the bell curve is fine.  But if we cap the game at 10 turns, for example, the after 10 turns hitting on 10s instead of 12s, a large pulse has done only 16 damage.  Yes, its 5 times what a PPC has done at just 3 damage, but neither weapon has done anything worthy of BV damage and the game is a draw.  Conversely, if the PPC needed 4s, and the pulse 2s, the pulse shouldnt be paying double for its 100 damage when the PPC did 91.  We should choose a more fair cost increase then 30% (existing) but below the double (the proposed system) as double price isnt a real representation of what target numbers the pulse laser will do real damage at.

Death from above used a graduated system, which has flaws, but the math was a +1 net TMM over base gunnery 4.  (It was a +3 tmm and gunnery -2, but net is +1).  So I think examining a +1 net to-hit mod (instead of your +3) will yield the most accurate numbers, including increasing pulse BV bonus up to 41% on a clan lpl from the too low 28%.

[Alsadius]

I do agree that 5 turns of ammo is rough, but 50 turns of ammo is too much.  I think alpha strike, at 10 turns, was best.  5 turns matches the existing BV cost for 1 shot weapons though, so I went for that since that's the current formula.  Also, its fair that every shot after 5 should be discounted more and more, as its less and less likely a mech is alive to shoot it.  Some exponential decay is the best bet, since a computer is calculating it.  Off the cuff, I'd say the average mech has a 75% chance of living to turn 10?  Id stop increasing the BV for ammo altogether at turn 13+.

Yeah, that was my proposal above. Exponential decay, from the first shot. After all, two one-shots is better than one two-shot(because you can fire them both on the same turn if you want), so the second shot isn't as valuable as the first.

For the 5 turn MASC rule, I like it as a simple 50% doesnt adequately describe how often you can use the system since you can MASC back to back, or on turns with no visible targets cool it down for no penalty.  So 3 times in 5 turns felt better then 100% (current) and 50% (the often quoted number).

Fair.

As for pulse, I see why you think its that good at the top end of the bell curve.  But what about the whole point of my math, which shows that pulse in your pricing makes a unit so expensive it can just buy -2 gunnery for the whole mech, instead of pulse on 2 guns, and be CHEAPER, using standard weapons with 2 gunnery instead of pulse.

You misunderstand my proposal. There would be no difference between giving every weapon -2 and giving the pilot -2 in this system, because the pilot's skill is included in the live calculations in exactly the same fashion as a weapon bonus.

This is where deciding on a turn limit can help.  In a "play till you die" game with enough maps, then the upper end of the bell curve is fine.  But if we cap the game at 10 turns, for example, the after 10 turns hitting on 10s instead of 12s, a large pulse has done only 16 damage.  Yes, its 5 times what a PPC has done at just 3 damage, but neither weapon has done anything worthy of BV damage and the game is a draw.  Conversely, if the PPC needed 4s, and the pulse 2s, the pulse shouldnt be paying double for its 100 damage when the PPC did 91.  We should choose a more fair cost increase then 30% (existing) but below the double (the proposed system) as double price isnt a real representation of what target numbers the pulse laser will do real damage at.

Death from above used a graduated system, which has flaws, but the math was a +1 net TMM over base gunnery 4.  (It was a +3 tmm and gunnery -2, but net is +1).  So I think examining a +1 net to-hit mod (instead of your +3) will yield the most accurate numbers, including increasing pulse BV bonus up to 41% on a clan lpl from the too low 28%.

What situation are you envisioning where a PPC is hitting on 4s and a LPL on 2s? That only makes sense to me if you plop two turrets down five or six hexes from each other. If you're getting that by god-tier pilots, then the BV penalty for pulse would be reduced accordingly.

[Atarlost]

Another issue is how overheat is handled and how overheating impacts defensive BV through movement penalties. 

BV2 does not discount the first weapon to go over heat.  An Awesome standing still outside small laser range fires its weapons in a 3-3-2 or 3-3-3-3-2 pattern.  If moving it probably uses a 3-2 pattern.  Current BV does not discount the third PPC at all because it's the first weapon that goes over.  It also picks weapons in order of battle value, not in order of effective damage per heat.  An AC-5 has less battle value than a PPC, but the usual assumption is that the Marauder uses the AC-5 with its 5:1 damage to heat ratio every round and alternates the second PPC with its 1:1 damage to heat ratio.

I think that if you're going all the way with computer assistance, defensive BV needs to be calculated per range as well because if a mech heats enough to hit a movement penalty its defensive BV needs to be recalculated.  This also allows stealth and TSM and any other toggleable system that impacts both offensive and defensive BV to be considered on a range by range basis.  TSM is complicated because it has to cool to turn off and return to normal operations so it might be treated as always on (but still calculating the whole BV twice because an effective +1 to gunnery and not being able to overheat might otherwise make it a freebie BV discount if you don't actually use it) but stealth armor would be per range. 

Picking correct firing patterns requires an explicit algorithm otherwise different pieces of software might implement it differently.  Judgement is also needed for how much movement heat should be assumed to be generated, possibly in the form of an algorithm for estimating how often a given mech is expected to be jumping vs walking vs running based on the relationship between its jump and run/walk MP, its motive type (stuff that sideslips probably wants to flank essentially never unless it has a lot of piloting upgrades.  I think that only effects LAMs for offensive BV unless quadvees can have hover movement, but the same logic also effects defensive BV for hovers and VTOLs), and how much defensive BV it gets from movement compared to armor, and whether it can do basic repositioning at walking speed (Urbies and Annies are at a marked disadvantage here). 

Calculating defensive BV per range alongside offensive BV is a ground floor thing that would probably be a lot harder to implement on the second prototype. 

[DevianID]

You misunderstand my proposal. There would be no difference between giving every weapon -2 and giving the pilot -2 in this system, because the pilot's skill is included in the live calculations in exactly the same fashion as a weapon bonus.

  Ah, so the pilot skill wouldnt be a set %, it would be pilot and mech dependent.  So a mech with very little guns, like a charger, could get a 0 skill gunnery for pretty much nothing.  Not sure how much I like this for narrative/campaign play since mech swapping is so common, but I agree its the most accurate way to do it.

What situation are you envisioning where a PPC is hitting on 4s and a LPL on 2s

  Beyond the simple short range no movement, it would also apply versus immobile things, or to pilots with upgraded skills.  A 2 skill gunner hitting with a PPC on 4s in an stationary awesome is a pretty common occurrence once battle lines are drawn and two players are in the 'beat each other senseless' part of the game.  But this point was made when addressing the problem of pilot skill using the existing +20% cost structures.  As you said above, your intention is to calculate pilot skill in the offensive BV part of the BV calculation.

BV2 does not discount the first weapon to go over heat.

  If you use my proposed rolling 5 turn calculation, this problem is solved.  You pay for the % of shots you actually make with each weapon in 5 turns, with a minimum 20%.  So the Rifleman example, you pay full BV for the 2 ac/5s and 1 large laser, pay 40% for 1 medium laser which eats up the 6 floating heat you are allowed in 5 turns, and the second medium laser and large laser pay 20% BV as backup weapons that are never efficiently fired in 5 turns, BUT could be fired at least 1 time in 5 (the alpha strike turn you die).  You still pay 20% for a weapon you never fire because you COULD fire it, once, like a one shot weapon.  If you use this 5 turn rolling heat calc, you dont need to refigure defensive heat calculation, as you only fire the extra weapons when it is an advantage--the turn you fire them, you have already moved, thus your defense is no worse, and next turn, if it wasn't an advantage to over heat you wouldnt do it, thus you shouldnt get rewarded by paying less defensive battlevalue for a weapon you only ever fire when it is a benefit.

For movement heat, im not a fan of assigning movement heat as a way to provide a heat discount to anything.  For example, a spider with 8 heat in jump jets pays extra for its weapons already because the jump jets increase its offensive multiplier.  But if you make it pay 8 heat every turn for the heat calc, then the extra heat will provide a steep heat discount when the mech ISNT jumping.  The spider will jump when it is advantageous to--offensive BV covers this already with the mobility modifier.  The heat the mech generates for the BV calculation should be the minimum heat needed to get the defensive mod it is paying for.  Most of the time this will be 2 heat from running, but some mechs have the same TMM walking and running, like a 3/4 mech which lost a MP from heavy armor, or a 10/15 mech that can walk 10 for a +4, so doesnt NEED to run to hit that TMM they are paying for in their defensive calc.  A 7/11 mech with 10 improved jump jets WOULD get the heat discount on weapons, as it pays for a +5 TMM, so the heat generated by that TMM should be factored into its 5 turn heat score.

To differentiate a mech like a spider 7m and 8m, identical except the 8m has 20 sinking instead of 10, I would add a heat weapon BV modifier section.  This is to say, if your mech got hit with +15 heat from infernos/flamers/whatever, what would you lose offensive/defensive wise.  This is where I would put your heat movement/targeting penalties.  Mechs pay for heat damage in the BV calculation, so figuring out what percentage your offensive/defensive BV should be lowered if you are vulnerable to +15 heat would take some trial and error, but that value can be determined im sure.

[Atarlost]

But if you make it pay 8 heat every turn for the heat calc, then the extra heat will provide a steep heat discount when the mech ISNT jumping.  The spider will jump when it is advantageous to--offensive BV covers this already with the mobility modifier. 

You're assuming that the mech never jumps in your weapon calculation, but assume it does jump in the movement calculation.  People use mechs with jumpjets because they do not expect to be able to achieve the modifier they're paying for in every round without them due to movement lost moving around or over obstacles.  Either you're pricing ground movement as if it's reliable and overvaluing it or you're pricing ground movement as if you don't always get to move in a straight line to maximize your modifier and undervaluing jumpjets. 

But if
To differentiate a mech like a spider 7m and 8m, identical except the 8m has 20 sinking instead of 10, I would add a heat weapon BV modifier section.  This is to say, if your mech got hit with +15 heat from infernos/flamers/whatever, what would you lose offensive/defensive wise.  This is where I would put your heat movement/targeting penalties.  Mechs pay for heat damage in the BV calculation, so figuring out what percentage your offensive/defensive BV should be lowered if you are vulnerable to +15 heat would take some trial and error, but that value can be determined im sure.

This is assuming heavy use of heat generating weapons, but if you're seeing heavy use of heat generating weapons in most games you'd mis-balanced the battle value of heat generating weapons.  Trying to use external heat effects to correct for non-weapon internal heat effects is going to come out wrong.  Maximum external heat is the same for all mechs, but jumping heat is not .  A Spider generates 7 or 8.  A Griffin generates 5.  Unless heat generating weapons are so common that their pricing needs to be reevaluated this is also going to overvalue things like the Shadow Hawk's 11th heatsink if it tries to compensate for not accounting for jumping heat that should be routine. 

[DevianID]

ou're assuming that the mech never jumps in your weapon calculation, but assume it does jump in the movement calculation

Nope.  Im assuming the mech uses whatever movement it needs to get the defensive movement mod it pays for.  So a shadowhawk, for example, is NOT gonna get 3 heat to discount its weapons.  A a 4/6/6 mech with improved JJ WOULD use its jump for heat discounts, as it needs to jump to get +3 TMM that its paying for.  If jump jet heat is allowed to discount your weapons, that is a problem unless the mech needs to jump to get the defensive PSR it pays for. 

I can give lots of examples, but if you cant agree that using jump jets to discount (sometimes heavily) your weapons when you DONT jump on a given turn, then we have irreconcilable differences.  Giving jump heat discounts when you dont jump just doesn't work.

This is assuming heavy use of heat generating weapons

No assumptions here.  Whatever defensive value is added to a mech to resist heat values, it would be calculated by the actual heat weapon usage.  Cant point that my numbers are wrong, they don't exist yet--but as a placeholder, it fixes the rare issue raised by the spider 7m/8m by slightly changing the BV of them, WITHOUT giving all jumping mechs everywhere free heat discounts when they aren't jumping.  The conceit the OP put forward is that a computer is gonna be required to generate these battle values.