Polyps are different. I had a small colony of pink buttons that multiplied slow enough so that one day I just looked at them and realized that they filled in really nicely. I got another small rock of orange buttons (probably 10 to 15 polyps) that spread like crazy when I gave it something to spread onto. I have another small rock of deep blue polyps that started with 6 polyps and is now above 20, but I can't get it to spread to other rocks. And still another rock with orange and green polyps that refuses to spread at all, even on itself.
I might try target feeding them though to see if I can get them going.