I don't understand experience gains at all. Several times I've been in Mage only battles, destroying several monsters using magic only, and the front row fighters got the level ups! This makes no sense at all, why are fighters getting experience for work the Mages have just done?
I still think that damage has a bit to do with it.
My human fighter levels faster than my minotaur fighter and I think that's because he deals more damage over time, compared to the minotaur.
My rouge used to level fast in the beginning and slower later on, as I didn't find any good daggers and had to switch to bow, all the while my mage got more useful and deals easily the most damage, leveling now almost as fast as my human fighter.
If it were entirely slot based they should level very evenly. I take care that everyone participates in a fight, if possible. So, if it were about participation only, my rouge and mage would level best as they never miss; were it about slot only, everyone would be kind of even, with slot 3 and 4 where mage and rouge are leading a bit; if it's damage based though it would make perfect sense.
Maybe it's a mix of it all and damage factors in by a small bit. Maybe I'm just imagining all of that.
[insert quote by popular deceased person you read somewhere]
I've gone ahead and tested it. You can test it yourself though in a few minutes. Just roll up a new party (or reload your save at start of game) and run to the first monster.
Try killing it with just 2 of your guys or all 4 or all 3. The result is predictable, those who participate get full xp, those who do not get 1/2 xp.
Updated my first post with all the information and explanation of how the experience system works. It should be a lot easier to read instead of trying to read all my other post in this thread.
Shameless bump but also about how to deal with the pack of four mobs and what it does for your experience for your group. It also tells how to maximize your exp against them. The first post is a long read but if you want to maximize your experience good read though.