I drive with the shaman as he is the healer and utility for the 4 warriors. I'm much less worried about positioning on them as they can take hits. If they die, I just rez 'em after; if my shaman dies or gets kicked/silenced, it gets a lot more painful. I have easy-access buttons that switch between shaman and designated tank characters if I need to position things more precisely. Until you get to fights where there are one-shot mechanics (Doan in SM Library comes close if you're low-30s), positioning really isn't all that critical IMO.