even if it's an unusually high amount, it's still possible to get it and is a trouble to get 1/3 of a level (1/2 for some level) from 12-13 minute of gaming is not normal at this level.
how you want to balance the exp at this range of level if it's possible to simply crush the ratio exp/time from any other content.

and the more important, it's in the 40-50 level that your class change the most.