From that rules link : "Travel must be in a continuous forward direction between TC1-TC2-TC3." If TC* are the zones described by GibSpmuh, then at last I get it!

As I said, this seems such a basic question from somebody who has just completed an AONE4 (and is already thinking about future OWEs ), but I thought the forward progression rule applied at the level of the six continental zones.

Hmmm, this is even better than I thought