I agree that 3MM should be PM and leave DM for earning. I think when the levels were originally set, there was no DM and PM was 100k. GM was 50k so it made sense that the LT PM would be double LT GM. Also there was still a bit of grade inflation in the system from the old days where every mile counted, regardless of source. Admittedly there were few sources/opportunities to earn. Now that PM is 75k, recalibration to 3MM makes sense to me.