So, I understand there is a bonus for having one class at a higher level. However, I'm not sure what this bonus actually is. I did some basic testing on my own, and it seems that you get the same bonus as long as one of your classes is of a higher level. However, I can see systems that would confuse the quick tests I did.

I'm just wondering if I should power level Arcanist to 50 first, or if it merely being at 40 provides the same bonus to level up all the other classes to 30. So does the bonus XP increase the bigger the disparity between your highest class and your current one? Or is it a simple 'on/off' kinda thing, and you get the same bonus whenever you're not playing your highest level class?