It may not be just a technicality if the only way the game can make a connection between two supply areas (one encircled) is by an airfield., you may actually need a building like a port or an airfield to make that connection.
well i suppose, that is the best one can hope for given the circumstances (if in game), hopefully a clever work around that modders can use that you suggested (if not in game), still, didn't think much was wrong with the older system of supplying from the air.