as someone who has tanked in most mmos i think the way you do it is fine, i do it the same way if im new to the place i do smaller pulls no matter what they say, if they cant handle an extra 5 min in dungeon then that's they're problem once i get better gear and know the pulls better i will pull some more. sometimes i will ask the healer what they want and of they say big pulls i remind them its 1 strike and out rule, ie if they cant handle first couple of big pulls i got to smaller pulls.