It's rather a matter of how the AI values its units and what is where on the priority list. In the first version of this mod, I had smaller field armies and more militia garrisons. The idea was that one or two epic battles could decide the war while you don't had to bother with garrisons.
But the first thing the AI did in each scenario was to disband its armies and sent those units to the remotest towns as garrisons. It then formed new armies out of the militias taken from the towns. Those armies, of course, were all commanded by captains. This made an extremely easy and boring game because with a single stack of proper field units you had no trouble whipping out all those militia armies. The reinforced garrisons then were not match either.
I was insofar able to deal with it by drastically raising the number of field armies and drastically reducing militia, that the AI now always has enough field units at hand, and never enough militia, to make armies mostly of field units only. But this did not change the general behavior of the AI. And the strongest unit the AI has in its arsenal is the general unit (even though cavalry is nearly useless in a town). I am pretty confident that if I would raise the number of family members the AI would start stacking them inside its towns. I have seen things like that happening both in RTW and M2TW.
Anyway, thought I would rush this out so that I can claim to be first to make an AAR: Regal Purple