How does the game decides whether the item is yours or not in uw/fow?

as above,if u say by how much dmg u contribute,then how about the monk and the battery necros,they don contribute lots of dmg,what they do is to heal/surport.

thx.

i actually think it is more of a random generator type thing.
a roll of the dice, 1 u get something , with new roll of dice to determine what u get.

Its completely random, this topic has been done to death many times already.