The mod/set/force/etc AV commands affect any Actor Value/AVIF. Actor Values are things that modify the base actor/object stats like chem addiction, armor enhancements, limb condition, etc. I did a search through the Creation Kit and found a "FallingDamageMod" AVIF with this description: "Modifies incoming falling damage by this percentage. Example. This value is 15, incoming damage is reduced by 15%." I figured this was what was used for armor modifiers and perks to make you immune or take less damage so I tested it out with the modav command. After I confirmed I manipulate total immunity or not I assumed that your courser armor probably got the value stuck at 100. Hopefully this keeps your fall damage back to normal without having to reapply it over and over every time you play.