-In any 8 members party, if you party average level is lower than the mob level you are hunting at, then when you kill PARTY mobs, you'll get double exp. Example: Say you are hunting at Ujigi, which are lvl 50, and you have 3 party members one is 54, the other is 42 and the other 50. The average level of the party will be: (54+42+50)/3 = 48,67. So, as the average level of the party is 48,67, then you will get double exp when killing party mobs which are at a higher lvl than 48,67. Therefore when killing party Ujigi mobs(which are lvl 50), you'll get double exp.
-The 'best' difference of level between the member being powerleveled/farmed at your party and the monster they are being leveled/farmed at would be around, if I recall it correctly, 10. So at Ujigi (lvl 50) the best level for your char to be powerleveled there would be around 40, because 50 - 10 = 40.
This is what I know at least, don't know if there are other 'rules' related to this. Any question just ask.
