What Inner potential should I try to get?

I've had this line many times before (with 10% at Legendary rank) and after a bit of testing, it seems to be a flat multiplier, where x% is added on top of all other multipliers such as ACA, Enrage, and Chance Attack.
EDIT: I believe Rare and Epic rank gives 2-5%, Unique rank gives 6-9%, and Legendary gives 10% only.

I got +8% of damaga against tagerts with (in my case) blindness, thats when I realized it might be equal to +8% total damage or something considering any boss I'll be fighting will have blind from panic on it.

Is it right to assume that 8% damage on blinded enemies = 8% total damage?