My experience is that my Regal wiped out my Zoanthids. It nips rarely at SPS and causes no damage. Fleshy LPS such as open brains, Acans and Lobophylia, etc are very tempting to most angels and can be harassed to death so I am not able to keep these. It leaves my Frogspawn and Goniopora alone. My Regal ignores my healthy clams but has targeted clams in decline. They have a strong sense when a coral or clam is not healthy and they will pounce. Keeping your corals in top condition with great water quality and parameters, lighting, etc. helps a ton. IME the Regal is one of the best angels for a mixed reef and they are almost completely harmless in a predominantly SPS reef.