They also speculate that the mucus is being transferred between polyps, which could happen in a colony of duncans, but again, that would mean ingestion of one mucus from the other.
From personal experience, I can tell you that the heads that get fed more, grow faster and get bigger than the ones that don't. But that's just anecdotal.
So lets talk a little biology on duncans... Duncans are made up of two parts, the stalk and the polyp head. The stalk is alive, and is covered in mucus. Usually pretty green. It generates skeleton. The polyp head is at the tip of the stalk. It can retract in to the stalk a certain amount... But the rest of the stalk is pretty empty. Fragging a duncan stalk reveals this. So either the duncan is spreading the nutrition through the stalk material, which sometimes doesn't connect with the rest of the colony, and remember it doesn't have any kind of vascular structure, so the nutrition dispersion would be relatively slow, or it doesn't share nutrition with the other polyps. I admit though I'm not a biologist, and so I might be wrong on all sorts of levels here.