BTAs are not natural hosts for percs/ocellaris clowns. So, its hit or miss with perc/occelaris and a BTA symbiont relationship.
I had a pair of percs 5 years ago and 12 rose BTAs in my 180 gallon reef. The percs ignored all 12 roses and hosted in my large colt coral for 3 years. Then, one day they decided they liked one of the roses and made it home.
When I set up my 240 cube, I again had several rose BTAs and added a new pair of black ocellaris clowns. They immediately went to one of the rose BTAs and seem very happy there! However, I just added a small Ritteri/Magnifica and a large red haddoni. They are now going back and forth between the rose, the carpet, and the Ritteri. I'm not sure which one they will settle in.
So, as you can see, its really up to the clowns and what they decide to do. I think if you added a naturally ocurring host anemone to them, like a Ritteri/Magnifica or LTA, they would probably take to it quicker.
I'd give them some more time and see what happens.