As part of an US - Europe award reservation with stopover, that I have currently on hold, I'm trying to split one flight on the return, i.e. instead of flying XXX to YYY I want to fly XXX - ZZZ - YYY, where the distance XXX - YYY is almost (within 5 miles, depending on which source) equal to (XXX-->ZZZ) + (ZZZ-->YYY).
However, I have been told by an agent and her supervisor that this split is not possible since it exceeds the maximum permitted mileage. Challenging them then that my original routing had exactly the same amount of miles, I was told "your original routing already exceeds the maximum permitted mileage" ?????

I'm really confused, because I don't understand whether MPM can be exceeded if you get the right agent (I always thought MPM was one of the things even India couldn't exceed).
Also, is the MPM counted for each part separately (i.e. AAA - BBB can't be more than x miles, BBB - CCC must be within y miles, and CCC - AAA has to be less than z miles), or is it all added up and the total trip has to be under x+y+z miles?

Thanks
David