Funny... I was just going to post about my plate coral tonight! I've had a fungia (short tentacled) for about 10 days now. First "real" coral... not counting the zooanthids. Grim Reefer... you'll have fun watching your plate coral!
I'd agree with putting the bubble coral up on your rocks, but definitely keep the plate coral on the sand bed. I'd read how they can move, and thought, "yeah... sure!" Wow. What I saw tonight I was totally amazed with. The thing was really really puffed up and just when I thought it couldn't get any bigger, it got even bigger. The short little tentacles were barely even visible. Just then, it just kind of lifted up one side of itself and scooted about 3/4" across the sand, and slowly slowly deflated a bit at a time. My jaw just about hit the floor. Our 5-year old was watching it with me, and she ran away from the tank somewhat afraid! I'm still not sure how it did that. I felt like I was watching a David Blaine (illusionist guy) show on TV!
Anyway... I'd originally put my fungia in a lower flow area of the tank and with tonights move (coupled with a couple other moves it did over the last week, at night while I was sleeping!) it's now moved itself into a more moderate flow area. I'm interested to see where it ends up parking itself, as I assume it will move itself to where it likes it best. Perhaps yours will do the same if it doesn't like where you put it!
Oh... and it will eat mysis shrimp just fine. Either spot feed some right by the mouth, or land some out on the outer edges and have fun watching it get it to its mouth. But as mentioned previously, you don't need to feed it anything from what I've been told. If you do spot feed it, just make sure your shrimp are fed first. Dang things will go over and literally grab a mysis shrimp that's halfway down the plate corals mouth, drag it out, and scamper off with it.