Your damage will not decrease against the stronger bosses, so the coins and credits earned per round will stay the same as you were seeing before. Reputation is based on percentage of the boss's health, though, so that is why the rep per round will decrease. Over the duration of a fight against a stronger boss, each player will do roughly the same total percentage of the boss's health and roughly the same total reputation as with the weaker boss. The coins and credits received, however, will be proportionally higher (five times as much).