Mine change sizes during the day and usually shrink up a bit at night when the lights start lowering intensity. They don't shrink up to the point where they don't have anything sticking out, although I have seen that before. By morning, they are about mid size and late in the evening they'll usually reach about 10 inches depending on where they decided to get in the flow that day.
Do you have a pic of how big they get at times? If they are getting big during the day and just closing up in the evening, I wouldn't worry about it terribly.
I'm not sure if it's nitrates and phosphates. I could see how that might slow down growth or something like that, but I think something else is making them unhappy to close up that much - depending on how they look in the middle of the day.
I think it's your alk. Is there any reason why you have your alk so high? Also your calcium and mag is high as well. I mean in addition to alk being high, you get diminishing returns on it. Meaning the higher alk you go, the more dosing it takes to get there.
If you are dosing alk, calcium and mag, stop immediately. I'm not sure what salt you use, but I would suggest doing a 20% water change a few times, like every other day. I would drop that alk down to about 8.0-8.5. I aim for 8.3ish which lets me stay within that range pretty easily. I don't know of any coral/organisms that struggle in that 8.0-8.5 alk range. Once your levels return to normal, then you can start dosing again. Although from the pics, it doesn't seem like you need to dose. The anemones don't need or benefit from high alk and cal. Mine are both generally low in my anemone tank. Some coraline algae crops up and uses up alk and cal, then stops growing. I won't do a water change for a few months and it doesn't at all matter to them.