EVE New Citizens Q&A

I feel certain that this question has been asked before, but I couldn't find it in a forum search or on Evelopedia, so I figured I would ask here. =)

The compensation skills say they add 5% per level to their specific tank and type. Is that a direct addition? Like, if I have a passive EM hardner that gives 37.5% out of the box, will training to rank 5 Compensation make it 62.5%? Or rather is it multiplicative, making it (weak math-fu) ~44.5%? I'm assuming it would be multiplicative, but would love to be surprised.

Also in regard to passive hardners, is the stacking penalty the same as it is for active hardeners?

Just for some context, my goal over the next couple months is to get into an Abaddon, and I know they have issues with capacitor usage. With active hardeners giving 50% resistance, it seems to my newbie mind that I could get close to the same out of passive hardeners with skills, and free up more capacitor for pretty lazers. I also feel like I can't be the first person to think of that, and must be missing something. If someone could fill in the pieces I'm missing, I would appreciate it!

Edit: D'oh, must always specify. This would be for Lvl 4 missions, purely PvE. XD

Stacking penalty works same for all modules/rigs which are penalized.

For hardeners, each damage-type is calculated separately. The module/rig which gives best bonus for that damage-type is not penalized, 2nd best module/rig only gives 86.9% of its bonus, 3rd best gives 57.1% of its bonus, 4th gives 28.2%.