Been thinking on that, but assuming if ParkFans is right, they might be forced to have the four for the sake of boosting and increasing the momentum of the vehicles as the trains traverse past the MCBR. That way, they can make sure that the ride can move as it is best suited towards.
Especially for as the ride does the elements such as the inverted stall, so that way they could guarantee that the hangtime would remain consistent and at the proper speeds for each vehicle as it goes uphill.