Mine doesn't steal food from smaller fish (chromis,bi-color blenny). He actually seems to be more about the hunt. He rarely eats food from the water column when I feed the tank. He waits till it settles on the rocks and sand and starts picking away (so the 6line would probably compete with your Mandarin for food). I can't comment on clowns because my Cinnamon clown runs the tank. The only fish her size is the trigger and he doesn't even bother with her.