I think this is a good question. The prince is one pipe where the dimensions are particularly important and cannot be varied much. You don't see Dunhill making group 2 size or group 6 size princes, as they would look wrong. I've seen larger than normal princes and they just look "off" to me, even when the proportions are right. There's no delicacy or grace. And smaller ones look weedy and like toy pipes.
The Dunhill group 4 (4407) prince dimensions are ideal, to me, and I've been happy with every prince I've owned, from numerous pipemakers, that observed similar dimensions. The key is the length - 6 1/4 inches. In order to make the bowl size right and keep the proportions elegant, the pipe needs some length in the stem. But more than this length would make it look like a churchwarden and it would be wrong. Too short and it loses all the elegance and grace of the shape. At this length the bowl would have about a 20mm wide chamber and a nice roundness to the bowl with comfortable wall thickness.
The chamber dimensions are important, I think, because it is supposed to be a pipe with a shallow, broad chamber. The depth and breadth of the chamber should be reasonably equal, like a pot. This gives a smoke that is not too long, and allows complex or strong blends to play best - particularly English and oriental blends. Same principle as the pot, but a much more beautiful shape.
It's all my opinion, of course, and if you prefer something different I can't argue. But I've found this to be the one pipe shape, more than any other, where varying the size or proportions never works as satisfactorily.