The long-tentacle is more difficult than the short, but I don't know how much that says: my orange plate is a glutton and always extended.
Best thing to do for it: full light, on the substrate, reasonable flow---it can't feed itself if its tentacles are blown flat-over.
Params: 1.025 salinity; 8.3-11 alk; 400-420 calcium; 80 temp.
Give it a slice or chop-up of table shrimp, applied directly onto the disk. This should wake it up.
Make sure it's not being hassled by any fish.