MPM is, I think, actual miles plus 20% (to allow for connections). Has nothing to do with Freq Flier Miles.

To get an idea of when an MPM fare can be better to use, compare UA and AA from Atlanta to BKK. UA gives you all of the connecting points, AA leaves it up to you (but you must stay within the MPM). I got ATL-BKK one time routed ATL-DFW-NRT (on AA), NRT-BKK (on JAL) BKK-NRT (on NW) and NRT-ORD-ATL (on AA).

Never have quite understood, though, whether the preponderance of the tkt has to be on AA, for this example, or what.

This wkend I'm flying ATL-CPH. On DL, you could go (all on DL flight nos) ATL-CDG-CPH. But for the fare I'm flying (MPM), it's allowing other connx points (I'm actually flying ATL-MAN (DL) MAN-CPH (SK) CPH-ARN (SK) ARN-JFK-ATL (DL).