Plate can be placed on most places that have a flat surface. They require space for expansion in the night or sometimes during the day. Make sure that they don't bump into sweeping tentacles of a torch or frog coral.
I think a plate does best on the sand bed with plenty of space to expand. As far as eating, they can be fed on occasion mysis shrimp in the center of there bodies.
You will see them engulf it through the center and ingest it and later spit it out after they have taken all the nutrients from the shrimp. They only have one opening to eat and do there thing.
They are beautiful pieces to add to a reef, mine was just too big for my nano, hope you got a medium to small one. They are very hard and prefer not to be blasted with a lot of current.
If given a nice place to extend they will form a perfect circle. I miss my long tentacle coral, hope yours brings you joy.
Mike