After playing with this mod for a while, I have a couple thoughts.
Stacked combat is an interesting idea and shows great potential. However, there are a couple of flaws.
First, there are many cases where it's better to send a unit alone rather than a whole force, since you may get casualties in the latter. For example, sending a horse archer + spearman vs. another horse archer, often results in the death of your own horse archer since the enemy's horse archer will fight it before the spearman.
I understand the whole concept of flanking which you're trying to replicate, but there's also something called tactics. When you attack a horse archer, the figurative commander should know damn well that it would be much effective to send the spearman in first, or to get the spearman to protect the horse archers.
There's also the problem where even though you greatly outnumber an enemy force, you still often manage to lose a unit. For example, if I have 6 swordsmen and the opponent only has one, I often still lose a swordsman when attacking. That's ridiculous.
Finally, as someone already mentioned before, there needs to be some mechanism that allows a force to withdraw in the middle of combat. In vanilla combat, you can simply not attack any more if you're doing badly, but you can't do that here.
Overall good mod, just needs plenty of tweaking.