Made a picture for you, pretty sure the distances are right. Melee will get hit by AoE debuffs, but I don't think there is a way to avoid that. They won't get hit by -ga3 which is all that matters really. -ga Debuffs are either 15' or 17.5', I forget.. so just make sure your tank support are far enough back to not get hit by that. The bard can go in the middle to sing for the tanks as songs have at least a 10' radius; WHM can also do 1 barspell and hit both tanks. I do suggest you have 2 tanks, unless you have a puller for the summons, as astral flow>aerial collisionx3 can be painful. Could probably put the BLM on the other side too if you wanted.
The most effective party setup that we have done so far was 2 DD4 COR BRD parties then the tank party in the ally, then BLMs outside nuking summons. Few mages also outside giving the DD support. Our kill time with that was ~30min, can probably be improved but I'm happy with it.
TP moves are determined by distance. If it never leaves hate on the tanks, it will only use boost. If hate shifts to melee under it, it can use all its TP moves, including charm (will only hit those directly under it, and it usually wears off before the melee go to hit the tank).
http://img.photobucket.com/albums/v291/Ellatrix/JoL.png