yes i cannot see the coralites, but as you say its growing "fast" then my guesse is an encrusting gorg, porties grow very slow, and also dont have the color faviation in polyps to skele, but the possiblity of it being an encrusting Montipora is also kinda likely, was that rock wild cultured, if so where from? or from the LFS
still sticking to encrusting gorg though.