Had some ideas, put them down in some simple drawings.

25-man 3 tank positioning




10-man 2 tank positioning



Seems like the triangular position min/maxes movement a little better. Proabably okay to spread out just a bit while val (kinetic boss) is active, and tigthen up when tal (fire boss) is active to soak more of the fireball. Should be a little easier for healers too if all the tanks are in range for you all the time. Only people that should have to move when Kel comes up (shadow boss) is the melee dps camp.

I like this alot. The only thing I can think of that will change up the melee positioning quickly is the little vortex (w/e it's called). Shouldn't be too hard for ranged to just spread around it.