T5's can be very powerful, although the wavepoints aren't the best. The key to good t5's are nice reflectors and active cooling of the bulbs. The wavepoints have decent enough reflectors, but have no fans and are almost water tight which traps the heat in. I had the retro on a personal tank and we have a 48" fixture over a tank at the shop I work at, I'd keep acro's closer to the top, but monti's and other lower light sps should be fine down low.
Edit: forgot to add that with the retro's (which run much cooler) I keep acro's 24" down with good results, so they should be good to at least 12" deep with the fixture.