What exactly determines bolt shrugging?

[kuniqs]

Hi,

AFAIK, % chance to shrug off a bolt spell = (inherent monster's magic resistance %)-(PC's level/2).

However, on the wiki I read info that spell proficency reduces the chance, too.

I dunno which information is outdated. I also remember reading about Willpower score having an effect somewhere.

Is PC level the only variable affecting bolt shrugging?

[Grond]

PC level is the only thing known to change the chance of a monster shrugging off an effect.

Things that do not affect shrug rate: spell power, any of the 9 attributes, luck.