When creating mesh interfaces with the default one-to-one interface method, by default empty mesh interfaces (that is, mesh interfaces between two boundary zones that are not currently overlapping at all) are only created when you have only selected two boundary zones for pairing; if more than two boundary zones are selected, mesh interfaces are created only where the zones overlap. You have the option of retaining empty mesh interfaces in all cases, so that every possible permutation of boundary zone pairings results in a mesh interface: first, enable beta feature access (as described in Introduction) and then use the following text command:

define → mesh-interface → auto-options → keep-empty-interface?