Propagating Sun Corals

[carver]

I have had Sun Corals (T. coccinea) for about 6 months. The colony is in the shape of a sphere and I notice the new polyps develop from the side of the parent which enlarges the size of the sphere. Will the colony eventually spill over to neighboring rock? If so, can I selectively encourage this by crowding a piece of rock that I want to be the new host into the colony? Any othe suggestions?