Something I'm learning is if you intend to AOE the instance in large pulls (first time doing this kind of leveling), wait until the mobs on average are 2 levels under you. They are still yellow, however this seems to be the sweet spot where you can get away with massive pulls. If you do it same level or +2 levels I find you can run out of mana, don't do enough dps in time before they flee bringing help, or you take to great of spike of incoming DPS to keep everyone up.

Perhaps with more mages that's not a thing but running 2 Mage, 1 Lock for AOE in my group while my tank sits there looking pretty, That's the range I found works for me.