It is natural way how to burrow itself expand/deflate foot in cycles.
And she can be happy in cave if that is big enough so whole anemone can hide inside, something like balling of magnifica anemones, but LTA is doing it in sand/cave - it detract what looks like into that foot part of nem.
But if you have 3 or 4" sandbed, it would be happy there and after burrowing mine never moved.
And it like close to 0 flow. At least mine was not happy as soon as stream do not let her disc to be lying on sandbed by gravity.