Aw, he looks lonely.

If it gets real big and slightly paler, he's low. If he presses up against the plug and stays small, two close to the light.

You would want something in the middle, although I do like it when they get all big and round. I've got a few that have grown over an inch in vertical length to get around the shadow cast by another coral.

What you will be looking for is a little nub starting out at the base, should see one soon. Several of the plugs that I kept in the tank already had little babes coming out.