Instead of this, I'd rather they change how participation works. It will be extremely helpful to make it manageable getting full credit without a group.

Case 1: Player A solo attacking from 100%-0% of mob HP --- bronze credit
Case 2: Player B in a group landing a single attack --- full credit

Rank As are designed to be killed by a single group within a couple of minutes. 8 players and 60+ players are just too great of a difference to bring in any reasonable adjustment.