dude you sure itsa fungia?
Pic??
Ive had some pretty tiny ones, <1", in some moderate to heavy flow and never had one "drift all around".
And the bottom should be all skeleton, no flesh except around the edges.
Smaller ones all usually have the nub from where they broke off the mother...
I wouldnt glue a fungia, they like to "walk" around and find their favorite spot.... but if it finds a spot and stays for a while, you could maybe glue it to some rubble there.
They should be kept flat on the bottom and are adaptable to most lighting/flow....tho the reds like a bit less light than greens