Yes basically any combination could make sense. Especially
Eomer's.
Where TTT: Book one, deals with Aragorn and all against Orthanc, and ends in Orthanc.
TTT: Book Two, ends with Cirith Ungol.
To even get things more complicated. I found many parallels between the two Amon's. (Amon Hen and Amon Sul). For that information check
here.
Is it possible that Tolkien again is trying to draw parallels between the closings of TTT Book One and Book Two? Isengard and Cirith Ungol?