Sorry, I'm having trouble understanding this. If you don't want an aircraft to avoid your line of fire, don't use tracers. If they can't see it, that can't avoid it.
And why would the cannon do full damage to a Mech or tank at full distance but only half to an aircraft or infantry? If the cannon is so loose as to only do half damage at half range, it shouldn't do any damage at all at full range.
I'd just use alternative ammo and be able to hit at a distance.
It is a lower-tech weapon, and even without tracers a 'tight' weapon only does damage via a line of shots, which is easier to avoid vs a wall of shots.
It does not do full damage to a Mech or veh at max range. When firing at full damage you take the range to the target, double it, and that is what range band it is in. So if a Mech is actually at range 4 then the effective range is treated as 8. If the Mech or Veh is at range 7 it is treated as though being at range 14.
For example, the standard AC/2 that has ranges of 8/16/24 normally, when used as a 'loose' autocannon would have effective ranges of 4/8/12 for full damage.
The standard AC/5 that has ranges of 6/12/18 normally, when used as a 'loose' autocannon would have effective ranges of 3/6/9 for full damage.
The standard AC/10 that has ranges of 5/10/15 normally, when used as a 'loose' autocannon would have effective ranges of 2/5/7 for full damage.
The standard AC/20 that has ranges of 3/6/9 normally, when used as a 'loose' autocannon would have effective ranges of 1/3/4 for full damage.
So an enemy unit is at range 12, and the unit has a loose AC/5. The player wants to do full damage, so they take the range to the target (12), double it to 24, and look that up on the AC/5 range bands. This value of 24 is greater than the AC/5's long range of 18, meaning it cannot be fired in full damage. So the controlling character has to fire it in flak mode at range 12 vs the enemy Mech, hoping to do 3 pts of damage to it.
It does full damage at half range and half damage (FRU) at full range.
It is a lower-tech weapon that only needs to use standard ammo to get the full benefits. Basically one less thing for your quartermasters to stock, and the lower tolerances mean it can be built on lower-tech worlds and maintained more easily. Just send them some standard AC/5 ammo (or the plans for an AC/5 ammo factory) and the militia is good.
This is a militia type weapon, rather than a 'modern' weapon.