There doesn’t seem to be any rhyme or reason to the amount of exp I get for different difficulties. Supposedly Casual gives 0% extra difficulty exp, but I get 4,400 for it.
But sometimes I get 4,400 on Normal, or 11,000 on either, and on the handful of times I’ve done Hard I’ve gotten 11,000, too.
Is it based on the level? Do they have different base Exp granted, or something along those lines?
Did you check the difficulty on which your ally played?
Because below Brutal the situation when you’re matched with random ally which selected different difficulty level is not rare. And in such cases bonus XP is calculated as highest between difficulties of both players.
So, if you’re playing Casual and ally Normal - you will get bonus for Normal. And when you’re playing Normal and ally Hard - you will get bonus for Hard.