I have kept mine directly under the surface about 4 inches on my frag rack they love it! I have 250w hqi halides w 39w actinics and Cree royal blues on them.
Do you have par readings on that?
Here are mine, bad pics/Iphone with flash. First is under double ended 150w Radium at about 150 part, shot through glass. The second is under t5 in about 140 par, seem to like it. They are from Tenor as well.

