Cecil,

I keep my P.M. about 8-10 inches above the water, my tank is also 28" tall. I can bleach sps out in the sand bed if I'm not careful. I found it useless to keep it lower, as salt creep start on the P.M. plus it heats the tank up more than needed.

I would bet most people stating T5's should be only inches above the water don't have a ATI Power Module. These are very strong lights!