I certainly don't understand all of it. Zone 1 is clearly for F passengers and a couple of select rows in Y, regardless of Medallion status. Zone 2 is for medallions in other select rows. Zone 3 is for the rest of the medallions. Zone 4 begins general boarding. I think there are a lot of factors into the zone concept including the plane type and the load of the particular aircraft.

And Bruce, shame on you for trying to cheat!