I think when you crease with with polygons vs edges that have no surrounding geometry, its interpolating the edges with two different contexts (polygons border edges get creased works, but not able to crease border edges). In Max, there's a check mode to interp. edges as you'd expect.
Thank you. Max does seem to always have an answer to things. I'm going to think of it as the intermediate edges cause the edges to flow around the object and sucks them in, to suck them out, got to crease those suck edges. But are you saying this only applies with boundry edges? With an offset extrude, the edges seem to…