You have also assumed that the surcharge is paid by leg and not by ticket.

The example "Leg" at one hour would be a connector leg such as YYZ-YUL or YYZ-YOW where about 60% of the traffic has connected from another leg. The other leg is most likely [better than 50% chance] longer than one hour so the amount collected is not nearly as high. [Also take into account that the surcharge varies from $15 to $25]