195 is basic aura 24%~ average resistance per attack
when doubling it it does not go to 48% as it's a non-linear gain as some of the gain is in chance to fully resist and some is to take reduced damg.
just mouse over your resistance when it you use masery and see the % but remember eah spel cast on you will do damg somewhere on this scale.
Take full damg ---------------------- resit the % value on mouseover ------------------ fully resist
it's a standard semi circle graph with the top being to resist your char page %,
also remember this -> your resistance on your char page is against level 85 enemies. your boss enemies are 3 levels above and so it's as if you had a % or two less than your char page says.