From what i noticed, the exp you get os percentage based, not only for your level but for your role. I noticed that when I was queuing for 50/60 i initially was gonna go healer, then i maybe thought tank, when i swapped I saw the exp drop. Then when I switched to a DPS it went higher than the initial healer one. If thats how SE is doing it than thay pretty smart. Since it shoukd allow jobs to even out when trying to level.