well it said that if A/D >= 10 then there is a chance of 10 damage, and A/D = 1 then it will be an average of 5 damage. so far it has checked out from what i have experienced, usually if A/D >= 10 it gives 9-10 damage, and i get the feeling that the higher the ratio the more chance i get of a 1 hit kill, but no solid data on this. im still in the colonial age and only recently got the chance to have A/D > 10. but it seems when my boosted musket men hit catapults (50/3=16.6) it usually results in more 1 hit kills than trebs (50/4=12.5).