I also have tracked both USPS and UPS parcels as they travel back and forth between cities on either side of mine...
But one explanation has nothing to do with either service...If an air freighter/commercial flight has five empty 'sockets' and six pods filled to capacity, the skycaps loading that aircraft will strip one pod down on the spot and cram the parcels/mail into the other pods...regardless of where they are going...
As long as they're in transit, it's someone else's problem...
(Yes, I've observed this in person at the Buffalo NY airport)
