I've got 2 Crocea under 4x 55 Watt T5 HO's, 2 bulbs Actinic, 2 10000K. They're high up, around 10 inches under the bulbs, but I've been moving one down slowly to see how low I can keep them. The colors aren't as intense as when I bought them, but they're not browning out, and are growing really fast.
Hope this helps, I'll keep you updated about the Clam that I'm moving down, if you like. I'm hoping to have it on the bottom by the end of the month.