Interesting, on a recent flight I observed 9E using the space under 8D and thought that was obnoxious, since the later-arriving 9D was deprived of that space.

In the absense of the metal box, it seems that it should be 9D -> 8D, 9E -> 8E, 10F -> 8F. However the metal box makes it sort of an anything goes scenario. I think it's analogous to how FAs will stuff anyone's items under the last row of first when there is a wall.