Progress counts only when the player’s share of the damage dealt to the target
meets a minimum threshold. Use it to require that the player did most of the
work, rather than tagging a target someone else fought.
The ratio is the player’s total damage to the target divided by all damage
the target took: the player’s share, added up over the fight, not a single hit.
1.0 requires the player to have dealt all the damage (a true solo kill),
and 0 accepts any contribution.
