Maroon clowns naturally host in BTa's so I would think that if the bta is very young and small it could very easily become beaten up by an overly aggressive fish hosting it. My advice would be to ensure that the host anemone be allowed to grow to a large size before introducing it to the clown, especially an aggressive maroon. Even percs and ocellaris are known to be overly aggressive when hosting. Mine host a frogspawn and the candycane and the clowns are constantly rubbing against them, I am sure this behaviour would be detrimental to a very small young anemone.