if it gets all deflated and looks like hell for a few days and not being picked on by any fish or inverts, give it a peice of krill.
is what is probably causing it to look that way in the first place. Digestion takes allot of energy from an anemone, and therefore can quickly start taxing on it's health. Provided proper lighting, and what meaty foods it can catch when the fish are fed, that is plenty of energy/nutrition. IME
BTA's will start over inflating when they are target fed to the point of excess/stress, it's not necessarily "growth". They can also quickly become a nuisance this way, overtaking and killing neighboring corals.
sometimes when they digest food they will shrivel up till they are done then come back to normal.
I don't notice drastic retracting/shriveling w/ either of my BTA's, except when stressed. They will occasionally retract a bit while the lights are on, but not much. When fed they generally engulf the food, and reopen within 10-20 minutes. Bottom line, be very cautious about how much and how often you feed anemones. FWIW
BTA's are one of the most tolerant, IME
, of periodic target feedings although they are generally not required. HTH