I'm highly suspicious that for defensive capabilities, Might & Magic is using some sort of system that takes the total amount of Armor Class for the whole party and evenly distributes it and also weighs how good your defense is against how good you're doing in the battle.

The reason I suspect this is because it certainly seems like the damage amount to different characters doesn't vary greatly, even if one is wearing Plate Mail+2 and the other Padded Armor. But changed that Padded Armor to a Bracers AC4, and suddenly you'll notice enemies that were dealing 20-40+ damage per party member may drop as low as 9+ damage to each member, even though only one person changed armor.

Also, sometimes it's better to kill, kill, kill as much as you can in the first round of a fight instead of concentrating on one enemy or the enemies with the highest HP (although there are times when the latter strategies are better), because it seems like the game will think you're doing better if you kill more and you'll take less damage from the enemies. It also might cause the enemies to not receive an extra turn if they do manage to fell one of your own party members. Usually, if the enemies fell a party member, they'll get an extra turn before you get to go, and this can sometimes cause you to lose complete control of the battle as they might continue to fell your party members on each round, get another turn, and repeat until no one is left standing. But if you kill 4-6 of them and they fell only one of you, they probably won't get that extra turn.