I think it also depends on your lighting and the size of the clam. A smaller clam is not going to like super intense lighting but a larger one will. When i had my clam I had him about 3/4 of the way up the rock work. Unfortunately I am stupid sometimes and moved a rock and down he fell, yanking his foot and killing him. So if you put him in the rock make sure he is super secure and nothing can knock him down.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.