Saw this discussion in ls chat yesterday.
Wiki says
"use of feint before steal seems to up the successrate" (something like that, I can't get on wiki from work. Of course wiki is user submitted so you could put that doing an emote on a treasure chest ups the drops on a BCNM and ppl will believe it.)
So, 1 thf said something like, eva has nothing to do with steal. It's either success or fail.
Other thf said it's calculated between your levels and his belief was lowering the eva to something closer to yours increases the success rate.
I tried to do a search and couldn't find anything anywhere. (kinda curious since I'm leveling thf) Anyone know of any testing on the matter?