So, if we all are cooperating on a goal, then we all share a common scoring for that goal (being it the sum of the scorings for this goal of all the players) no matter who exactly got each point.
In the case of a reductive goal, it is the same, all the players reduce their scoring with the reductive goal a single kart get, so again there is asingle reductive coeficient (multiply the reductive coefs. of all the players to get it) that is shared by all the players.
This last point is not free of troubles: If a players dies, its redcutive goal for health drops to zero, so my own scorings will be all... zero! So I lost the joy of living and let the rocket fall down to ground and break... uh! not so good to cooperate in those conditions!
The following video shows a group of players cooperating on all theirs goals. The effect is not much evident just because one layer of intelligence only simulates five seconds or so, and it is not long enough to really appreciate the difference. I hope the use of a second layer of AI (not implemented yet) will make it much more visible.