Mostly the floor but the wife likes to stick mine all over the rock when I'm not looking. Shrooms are just like any other coral as far as finding the sweet spot .Some like less flow and light. Some don't mind flow at all. Some will detach and float away with just getting flow near them. Some hate light and some can't get enough light and grow into gigantic beasts and pop babies that end up taking over your tank. Just need to find where they like to lay out flat and bask in the sun.