Al,
next time you order out, let's buddy up on costs! Did you get my PM?
The short answer is that I think it will be OK on the sand with your lights. Croceas are rock-borers in nature, so in nature that is where they are found. They are found in clearer, shallower water than some other clams, so they are generally accustomed to intense light and may become browner under weaker light lower in the tank. Those are some considerations.
I keep my blue max higher in the tank under a 250W 6500K. The squamosa and gold max go on the sand and the gold max has attached through the sand. The squamosa never has. Before they attach, they will kick around some and try to get into a secure spot with a good orientation to the light. While doing this they fall off the rocks. One trick I used was to put the blue max in the concave side of a large horseclam shell, then fix the shell to the rock. The clam kicked around till it got oriented, then attached. But the clam got bigger and bored into the attachment point, and after 10 months it snapped the shell into pieces when it was flexing shut.
A better method is to take out the rock that you want the clam to attach to, and using a hacksaw, saw a groove shaped for the clam into the rock. The groove tend to keep the clam on the rock until it attaches, unless it really wants to move.
If you see a clear snot starting from the base and going up the side of the clam's shell, I think it is making an attempt to attach. I've seen the snot prior to a clam becomming attached.
Have you considered feeding and would you be interested in feeding
Instant Algae? I've been want to use their coral and clam diet product, but am not willing to pay shipping on small quantities. Maybe we can organize a group order? I know of at least one guy who uses it in Kitsap and he knows other guys...