Migrating Mushroom Corals

Greetings-I have a 120G reef tank established about 5 months ago. As a
retiree, I have been patient about adding things and have put in mostly soft
corals and recently 2 clowns, 1 cardinal, 1"exquisite" wrasse, and enjoy
watching things develop.About 1 month after set-up, I added about 75 hermit
crabs, and recently a Mithrax green crab and a short spined(?) sea urchin.
Chemistry in tank is checked on a regular schedule and seems fine. My
question is about mushroom corals. About 4 months ago, I added a live rock
with 15 or so purple mushroom corals with some hitch hikers. They seemed
happy and slowly waving in the soft current. About two weeks ago, I noticed
two mushroom corals on the top of the sand in the back(black)end of the
tank. Have not been able to see that any are missing from the piece of live
rock but the two new guys (?) seem happy on top of the sand and actually
move around a bit within a 5 or 6" area, perhaps from current flow.
Question--will these guys establish themselves on some of the other live
rock? Will they be o.k. hanging out on the sand--it is a part of the back
of the tank that is difficult to access. Should I intercede and try to put
them someplace--my guts tell me to let nature have its course. Is this
typical of mushroom corals?
Thanks in advance for any advice.

--
Al Waitz