You could try making it close up a bit so it's not as dense and take a macro shot, then you can count how many tentacles are on it per polyp. If it's an encrusting goniopora it'll have 24 tentacles per polyp, based on what I just researched porites should have 12 tentacles? We can safely dismiss alveopora simply because of the polyps themselves, the tentacles would be more rounded on the tips whereas those are more tapered. Based on what I can see I believe it to be a encrusting goniopora simply because of the density, porites polyps generally aren't as thick and because they have less tentacles the skin itself should be showing.
Sorry I'm a bit late, but congrats on the sale.