Alright, I want a perk that straight up reduces damage by a flat amount, like the "Damage Threshold" concept seen in the Fallout games. To do so, I made the following perk:

Entry Point-
Mod Incoming Damage --- Function: Add Value
Value = http://forums.bethsoft.com/topic/1444098-the-mod-incoming-damage-entry-point-will-this-work/Value + (-5)

For conditions I put in the standard "wearing all heavy armor" conditions found on many of the heavy armor perks.

So will this work like I want it to? My concerns:

1. That this will take effect before the enemy's multipliers, making it far more powerful than intended. I intend of making it 3 tiers, with values of 5, 10, and 15 at HR levels 30, 60, and 90. Having an enemy's BASE damage reduced by 15 would be FAR too good, but having their TOTAL damage be reduced by 15 is far more reasonable in the late game. Any idea how this will be factored in?
2. If this perk reduces damage past 0, will it heal the player? I don't want that.
3. Can I even use a negative value in the "Add Value" function?