ToME: the Tales of Maj'Eyal

A while ago in my current game, I headed off to Tempest Peak. After killing a certain boss, I started strolling around opening up vaults. The final one I entered contained a Lv32 storm wyrm (I was Lv16 at the time), which I got trapped with, but finally killed a few turns before my recall kicked in, by luck. I did not level up from this : killing a monster that was twice my experience level.

How does ToME decide how much EXP you get?
Are there monsters that you just get no exp at all from? (eg summoned ones)

Experience is strongly dependent on enemy rank, so when you get jumped by something with stupidly high level, you don't get much experience for being able to beat it up.

Thanks, that's really useful to know