Lol guys, killing the little newbie (his words, not mine) with your ubar leet triggers. It has to do with the level of the unit. You know how creeps show their levels when you mouse over them? Same thing.
The field is something like Stats - Unit Level. Under Advanced - Gameplay Constants (I hope that's it, no WE on this comp) there exist several fields with Unit Experience in their names.
There is one called something like Level Factor, the one that you want has a default setting of 25. That 25 is how much experience regular units give per level. So then a level one unit gives 25 EXP, a level 2 gives 50, etc.
There is a field however, that modifies that to give a percentage of the other field along with the bonus, I'm sorry that I don't know either the name or default, you will want to set that to one.