It sounds like what you are asking is essentially to make overkill wipe out any advantage the smaller unit may have due to better training or equipment, but I'm not entirely sure.
Perhaps you could rephrase with these existing terms in mind?
Thanks for the difference between the two terms! Revised to reference overkill where I spotted it.
What I'm actually asking for is slightly more complicated. Not knowing how the game actually calculates these things, I'm going to make a few assumptions to illustrate:
1. The effective combat ability of a soldier is directly related to Training+Cohesion+Weapons+Armour (I'm sure this is horribly wrong, but it makes my math easier).
2. So, a good troop of soldiers with 70% on all those stats has a strength of 2.8 (.7+.7+.7+.7 = 2.
, while a crappy troop with 20% on everything would have .8 (.2+.2+.2+.2 = .
.
3. So, with our above troops, our really good troop has a strength of 2.8, vs the 3.2 of four attacking crappy troops, and he gets cut down. He takes two, maybe even three of the attacking crap troops with him, but he and all his friends still die.
Now, this is a vast oversimplification, not taking account how the game actually calculates strength, nor any morale or banners or anything, but it gets my point across: The point where overkill should kick in is long after the point where superior numbers will beat superior quality
in an open field.