I'd read about keeping an eye on 'em, and the fish had been in the tank with a previous blue and gold maxima that ended up dying, but I never saw him touch that one. He just suddenly copped an attitude with the new one! Hate it when that happens!
Don't place your clam in the main area claimed by the clown, either- my Gold Stripe Maroon pushes things out of her area or picks up rocks and such things small enough to carry and moves them out!
Just my experiences....my Coral Beauty ignores the clams and I've also heard/read that they are clam nibblers sometimes. It depends on the individual a lot as well. My Hippo got to @ 5" before he started, also....