But, does 'point' of origin mean airport or city?

It used to be, I think, that multiple airports in a given city were considered 'co-terminous', such that you could transfer between them without regard to your xONEx. In that view, what you want would clearly not be allowed. But now they are differentiated, such that transferring from e.g., IAD to DCA is now considered a ground segment and one of the 16 allowed sectors in the ticket. Arguably, if the point of origin is the airport and not the city, your idea is logical. Unfortunately, the way these things usually work is that the rule is interpreted for the advantage of the system and not the pax, so I wouldn't hold out hope. But good luck!

cheers,

Henry