Short Tentacle plate question

[donkeys4hire]

I've had this plate for over a year. Tentacles won't come out. It hasn't gotten any bigger either. Its seems to eat food ok. 55g mixed reef all parameters in check. Any ideas on this issue.

 

[milesofreefs]

tbh ive seen so many plates that are just like that.
but it could be a flow problem maybe to much flow...