I have a couple different clams. When I got them, I placed them on a 3 or 4 inch piece of live rock with a natural indentation in it, where the bottom fits and it sits naturally. The clam attaches its foot to the rock which comes in real handy when you have to move it, want to experiment with lighting and location, cleaning the tank and so on, without fear of damaging the clam.
You know I read this too. I was originally going to place it up high on my LR as I had the perfect spot for it. Indented and all. But then it was suggested that the SB was best. But now I'm thinking about it's foot becoming attached to the glass bottom and I'm not liking that thought at all. Soooo tomorrow she goes on a piece of LR all of her own. Thanks MyNemseie!