Mine is acting a bit like that. It was opening fully until about 15 days ago, all polyps open most of the day but much more late night with long and fat tentacles. Now all the polyps are still opening, their mouths are pretty visible when feeding, but the tentacles (not the polyps) are much shorter. It seems like someone "trimmed down" them, they are much shorter in length although every polyp displays their tentacles, just not as long as they were. It now looks like they have a little "crown", it's actually pretty as well.
Is it possible that they don't extend the tentacles fully if there is enough offer of food already or if the polyps are already well fed? I didn't change anything in the feeding routine. The only difference that I've made in the last few days is a cleaner tank water - the levels of phosphates were pretty high (I wasn't using a deionizator in the first months...) and I've reduced them a bit using resin. There were no other changes in salinity, gravity, pH, KH, temperature (maybe one degree Celsius higher, it's the middle of the brazilian summer) etc. This coral is here with me for about 4-5 months.