Dong, I don't think they're that picky - until it comes time to feed them, then shut all pumps (waterflow) off. Otherwise, put the rock in a separate container during feeding time, and feed away.
Mine are in medium/heavy flow area but somewhat sheltered in a cave mouth.
I feed them once a day with a mysis, bloodworm, cyclopeeze mix. The number of polyps have tripled in the 3 months that I've had them. They like to eat!