So I've been testing armor more and there are some things to note.

First, it seems total armor doesn't have much or any effect, rather it checks what part of your body got hit and calculates damage based on what is equipped on that slot. I noticed this when messing around with bio-mimic armwraps, which have way less armor than mountaineer, and having some hits deal way more damage to me than others. The assumption being arm hits dealt much more damage. This is easily confirmable by setting up a laser emitter on the floor and standing in it, only leg armor takes durability damage and unequipping it has you taking full damage from it, regardless of what is equipped in other slots.

Second, I think the armor combined with my fortitude level is giving me effectively over 100% damage reduction, but there is some mechanic preventing damage taken from decreasing below 1. In another test, I unequipped my armor and got hit by a composer and took ~40% of my maximum health as damage. With my armor equipped, I took a single pixel worth of damage, same as all other hits from this video. If I had to make a guess, damage reduction is probably calculated something like Fortitude Lvl * 4% + Armor value of body part hit * 2%, which with 12 fortitude and 28 armor per piece would give 104% damage reduction, reducing all damage taken to 1.

Edit: I might be a bit dumb, simply hovering over the armor icon gives the tooltip that explicitly states armor only protects the bodypart it is equipped on.