In addition, my new priority is trying to eliminate as much "modifier math" as possible. That's part of the underlying motivation of writing the shield rule the way I did. The problem with allowing helmets to use the same rule as shields is: what do you do if you have both a shield and a helmet? I don't want to add the two effects and block all damage rolls of 2 or less. So what I think I would go with for helmets is the following:
Targets wearing helmets ignore any damage roll of 1, as for shields, unless the attacker is aiming for something other than the head. This does not stack with the shield bonus, but does work against backstabbing or other attacks that ignore shields.Also, since I allow critical hits to cripple the head, I'd allow a helmet to reduce or prevent the added injury. You won't automatically get your head smashed in on a high damage roll to the head if you are wearing a helmet.