Guild Wars 2

So after you hit the seal, archdiviner gets stunned if someone is staying within a certain range of the boss.
Not sure about the effect radius, seems about 240 (like shadow refuge, didn’t really test)

The formula for how often he gets stunned is: 2ab

a = person/s in instance
b = person/s around him (dead people stun him as well, summons don’t matter)

Examples:
Solo (a=1) and you stack on him (b=1) you stun him 2 times,
4-man party and 3 person next to him = 24 stuns

So in a 5man party:
10 stuns per person, 6 of them do basically nothing besides guaranteeing that the boss is disabled, going from 5 stacks of defiance to 5 again.
So you just have to remember the remaining 4 stuns:

5 stacks of defiance and 1 person around him = boss will end up with 1 stack
4 defiance, 1 person = 0 stacks
3 defiance, 2 persons = 1 stack
2 defiance, 2 persons = 0 stacks
1 defiance, 3 persons = 1 stack
0 defiance, 3 persons = 0 stacks