I’d try placing your BTA right in the middle of your clowns favorite spot they may move away from it and nip at it at first but after a few day they should move in. BUT don't be surprised if your new Anemone chooses not to live where you’d like it. Sometimes they’ll move around a bit before they find “the spot” they like. Take note of this spot because if they move from there something has changed and they’re not happy. They may find a new spot after a move but if they constantly roam after “nesting” worry because they’re not happy. Check water quality, light, food, and current strength/direction changes as causes of movement. Don’t discount predation (day or night) by tank mates if your clownfish don’t bond with the host. I have been very lucky bonding my hosts to mated pairs. I hope you the same.
Above all use foam intake covers on all tank intakes to guard against Anemone SUCK! It only has to happen once for you to understand the term in detail. Imagine your new Anemone blundering into or near an unguarded intake it will be ripped to shreds on the intake grating. It doesn’t take much damage to the Oral disc, column or tentacles to kill them. A foam cover lowers the damage (if any) your anemone will incur. Good luck.