What I find naturally in my reef is that the Yumas find spaces on rock out of the current. Mine walk around like anemones do. It's scary to come down one morning and they are gone. But so far every time...they reappear on the end of the rocks towards the drains..out of the way of the direct current. They seem to know where they want to be and get there.
And whether it is in my reef tank or in my large frag tank...they all want fairly low light. They like it dim, near the bottom of the tank or at least in the less lit parts of my frag tank. I always have half my frag tank well lit and the other half with the lights hanging about 3 feet up. I let coral tell me what it likes best. The lit half of the frag tank has the lights about 6 inches off the water...with the water on ly about 9 inches deep. SPS gets blasted there.
But I find some things can adapt to being there too. Like Acan Lords will adjust to it if slowly acclimated. And if they do it, I am often rewarded with huge cool color shifts.
But anyways I have done a couple things with mushrooms. I take clean chinese food plastic containers. I poke loads of holes in them so they have decent flow. Then I fill them with reef rubble and mushrooms and submerge them. After a few days, the mushrooms have attached to something. Then I can glue that piece of rock where I want it. If the mushroom doesn't like your choice, it will move itself. The other thing is to take a container.....put the mushrooms in it and cover it with an orange bag. You know that plastic mesh oranges come in? Then rubberband it tight around your container. It lets the water come and go but holds the mushrooms in place. It may get algae on it. But you are only using it until the mushroom attaches to the rubble.
Good luck. Trust the mushrooms. They seem to figure it out for themselves. Oh the other thing is I have glued toothpicks to frag disks or onto the reef...and then stabbed the mushroom onto it...then bend the toothpick down to make a loop onto the rock or frag plug. That can work too. Just go low flow and light and you'll be fine.
