I'm going to set aside meta doctrine and go back to in-universe doctrine. I'll be making the same argument I made upthread that the DCMS just patches ad-hoc C3 networks together immediately before battle rather than deploying units with pre-arranged network assignments, but I'll be doing it in a new way.
If we look at a 4 unit C3 (sub)network, from a technical standpoint it's required to have a C3M. Beyond that, the three slaves can be anything. But for maximum effectiveness, you'll want some mix of spotter(s) and heavy damage dealer(s). If you're scaling up to a full company size network, you're looking at exactly 4 Masters and either 8 or 9 slaves, depending on which of the 4 legal configurations you're using. While the Master units can contribute some firepower, you'll still be wanting limit their vulnerabilities (and therefore opportunities) and so of the 8 or 9 slaves you'll still want a decent number of not just spotters but also damage-dealers. I'm convinced that it's a good idea in the game (and therefore in in-universe doctrine) you'll want to split your available slaves as close to evenly between spotters and damage-dealers as possible. You need as many spotters as possible because if you're able to keep your Masters from being popped or jammed, then your spotters certainly will be the target instead. If you're losing a spotter per turn, you'll want at least 4 spotters to keep the network going over the course of the impactful part of a game. And of course you need as many damage-dealers as possible, or else the whole C3 advantage is moot.
So if we have 4 spotters, 4 damage dealers, and 4 C3M units in the network, that's pretty neatly a Recon/Skirmisher lance, a Battle/Fire lance, and a Command/Assault lance. No need to figure out how to fit a C3M unit into a recon or pursuit lance, or to figure out how to fit a spotter into each coterminous lance/C3 subnetwork.
Of course, the above is describing Configuration 1 where there are no dual C3 Master units in the network. If you do have one and you use Configuration 2, then you have a spare slave. An extra damage dealer is probably the way to go, but certainly not cut and dried. Either another spotter or another damage dealer can work. The strength of C3 is that it's strategically fungible... if you assign 3 slaves to one Master there's absolutely no requirement they have to retain that relationship in the next battle.
So maybe your battalion that's able to field a company sized C3 network actually has more than 4 C3Ms in the bn, and/or 10 or more slave units. Plug and play the network as you'll need it for your impending battle.. that's how it's meant to work! Besides, having a few "extra" C3 mechs across the battalion allows you to absorb some attrition and still field full sized networks during the campaign. Of course, if you do have 5C3Ms and 12 slaves, you simply can't prearrange their network relationships. It's just not technically possible.
Another thing to factor for in-universe considerations is what else the DCMS has in abundance besides C3.... Omnis. C3 configurations 3 and 4 are not even possible given canonical designs (requiring a triple and quadruple C3Master, respectively) but in-universe, you're not limited to tournament-approved configurations. if you've got 9 C3S units on hand but no C3M... put 4 of them in a Sunder and BAM instant company-sized network is possible! The fact that Omnis are a thing and is reason enough alone for me to feel confident that in-universe they don't pre-arrange their C3 relationships. Any Omni is automatically capable of filling in at any needed part of the network.
Edit:
Another thought about C3: In Alpha Strike it does something else that isn't represented in Total Warfare/BattleMech Manual... it helps with Battlefield Intelligence. The MHQ special is giving you a benefit even if there's no network. Looking at in-universe doctrine, it may be more attractive to spread your C3 assets across the regiment rather than concentrating them in one battalion. Or maybe it's more advantageous to concentrate them for a massive advantage. I suppose it'd depend on the regiment's CO in question.
