According to patch notes:
6 Man party = 50% exp bonus
7 Man party = 100% exp bonus
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I don't see it...
it looks correct.. check my math below using your xp amounts posted:
XP per mob / party / bonus / xp/toon
1249948 solo 0% 1249948
312480 6party 50% 312487
357120 7party 100% 357128
Math below for example
6party = xp (1249948*1.5)/6 = 312487
7pary = xp (1294448*2)/7 = 357128
The difference in the xp displayed vs calculated might be due to rounding errors.
I am assuming that all toons in your party are level 83 with vit4 and no additional xp bonuses.
Under the old xp bonus rules as stated in patch notes:
XP / party / bonus / xp per toon
1249948 solo 0% 1249948
312480 6party 58% 329153
357120 7party 63% 291059
Math below for example
6party = xp (1249948*1.58)/6 = 329153
7pary = xp (1294448*1.63)/7 = 291059
Again if my math is correct.. under the new rules.. 7 toon party of equal levels has more xp per mob - vs the old rules a 7 toon party; but old rules 6 toon mob gets more xp per mob vs 7 toon party.
Yup, it is important to understand that the increase from 50% party bonus to 100% party bonues does not mean that every single party member will suddenly get 50% more xp for every single mob, because of course you also have one party member more now, and that "eats up" a lot of the 50% bonus.
6 man party with 50% bonus: 312487 per party member
7 man party with 0% bonus: 178564 per party member
7 man party with 50% bonus: 267846 per party member
7 man party with 100% bonus: 357128 per party member
So it is correct, the 100% party bonus of a 7 man party does give you 100% more (than a 7 man party without bonus).
Other way of looking at it:
In a 6 man party, everybody gets 150% / 6 = 25% of the mobs unmodified base xp.
In a 7 man party, everybody gets 200% / 7 = 28.57% of the mobs unmodified base xp.
All of the responses to the original post are correct. And, yes, the "(Bonus)" XP details in the system message apply only to vitality boosts such as Nevit's; the XP change according to party members is a change to base XP, not bonus XP. (Some players might think it is a bonus because it is a positive change from Freya to High Five.)