i still say to start them on the sand, well OK then, you made your point.
They can be started ON THE SAND and ON A FLAT ROCK.
If the clam came from the similar set up or brighter, move them to where you want it to sit. If the light was not as bright, start them lower in your tank.
My crocea is under 250's at 15K. I have it half-way in my 90, right under 1 light.
Good luck with it.