Thanks gentlemen.
Ron, I have noticed that in some of the best looking tanks I've seen, many acros are not shy with their polyps even during the day. To me it is as though the coral feels comfortable with polyps extended most of the time. It's probably not being nipped by fish or chewed by pests.
More polyp extension equals more surface area which during the day could mean more photosynthesis yielding more photosynthate and thus more energy for the coral. Just a thought.