I have a lunar wrasse in my FOWLR
(5x2x2) with a volitan lion, striped puffer, miniatus grouper, and Niger trigger. All get along well and they are all between 5 and 8 inches at this point. The lunar wrasse is very active and aggressive feeder. He was a but aggressive with smaller fish and nipped their fins quite a bit (I had to move a spotted grouper (3-4") to another tank as it got excessive). So with my experience (just mine, not scientific or otherwise), I would recommend that the wrasse is same or a bit smaller in size than the tank mates. Otherwise he is really cool to watch and is quite fast when he ticks off the miniatus grouper.