Ok, so if I understand you correctly...
Let's say we have a party of 4, with one level 6 (36), two level 5 (25*2), and one level 4 (16) characters (Y=102).
They win a fight with a CR of 5, which is 7500 raw XP.
7500 / 1200 = 73.53 (do you round down for this? I'll assume it does for the...