To be honest, I'm not sure exactly who has done this (maybe IATA) but some organization has determined what the maximum permitted mileage is for a given city pair. When an airline quotes a mileage fare (which is generally higher than other fares offered by the same airline, b/c it offers more flexibility in routing and offline connections, etc.) that fare is valid for journeys from origin to destination for up to that mileage level.

You can then go over the MPM (I think by up to 20%) for additional surcharges.

Answer to your question, unfortunately, I don't know. The way I read it, you're only able to make 2 connections (between other airlines) but as many connections as you want on whatever carrier this is.

My guess (and it's just that) is that you wouldn't be able to go from an east coast city to a west coast gateway b/c this is an instant purchase type fare, so the MPM is probably very close to exactly the shortest distance between your two points, e.g., if this is a CMH-LHR fare on UA, the MPM is probably such that it is almost exactly the mileage CMH-IAD-LHR, and if you wanted to go through ORD, you would pay the mileage surcharge.

Good luck (although I think this stuff is sort of fun - I don't play chess, I play fare construction games).

Greg