small clusters grow new buds faster because there are more edges for them to grow out.
i.e. if you have a single cluster of 50 polyps, being that new polyps will only popup on the the outside edges, all the polyps in the center of the cluster do nothing to propagate more. So if you took those 50 polyps and broke them up into 10 smaller clusters, you'll get5 more growing.
make sense?