Don't worry about it now. A lot of SPS need to mature and actually grow polyps to a larger size before it really becomes noticeable. There isn't giant polyps in there hiding waiting for just the right sweet spot. It also depends on the coral. Some like stags (very broad statement) don't have big polyps and sometimes don't display them much at all. Sounds like you've got your water maintenance and stability down now if your getting growth and color. Just be patient and they'll grow/reveal themselves when they're ready. Broadcast feeding isn't bad, but be careful. If this is a new thing you're doing you don't want to throw off the nutrient balance right when you just found the sweet spot for growth. Color and polyps will follow.
FWIW, some polyps are mostly nocturnal too, like my vivids colony I just got, I noticed that it hasn't grown all its polyps out yet, but the tips have large polyps only visible at night, and normally the colony has small polyps about its surface too. So this could be something you're noticing also. In contrast, my other corals and especially my RMF biohazard has polyps that look like they're morbidly obese flying around all day.