mantle extension

I have a new crocea clam. Its mantle is extended but it’s not covering the upper part of its shell. Is this ok? Is it receding?

Hello! Fairly new at reefing (going on year2) and i recently got a clam. Side note before i get into this: I am waiting on an ICP test and will list my parameters at the bottom. Now for the narrative: It seems happy for the most part, but recently it seems to have moved itself 180° degrees, and...