JammedStab
I think GURU on page 1 explained it all perfectly.
Just so that you're aware, if you do a ULR, you'll get paid for the full duty regardless of bunk time. However, you only get credited with half the flight 'stick' time when you augment. So, for example, a flight from DXB to LAX has 4 crew (2 Captains & 2 F/O's). One crew will be the operating crew out, the other will operate back. The operating crew are basically the ones who do the take off and landing and half the flight. The augment crew do the cruise portion only. Say the flight is blocked at 16 hours both ways, then all crew get 32 hours flight pay for this trip but only 24 hours credit for actual flying hours.
This is known as 'factoring'. It was initiated by the GCAA to ensure cadets or low hour pilots could not use bunk time to count towards hours for upgrade. In a rather unusual and somewhat surprising move, Emirates have interpreted the rules and regulations differently.
Much like crew report times, ULR definitions......etc.....etc.....
Hope this explains it!
Harry