Blastomussa growth
 

I have a couple of Blastomussa clusters and am trying to find an answer to how they spread. Back when I first purchased them, they seemed to have some room to spread on the small rock. At this time they have completely filled up the rock 'frag' and I was wondering what's next. Do they continue to spread by adding more skeleton to the rock and in effect increasing the size of the rock?? Or do they need another or a different rock to spread to?

Any help would be appreciated.