It IS possible to get roosted with them backwards........I did it to Nick unintentionally. 'twas ok, but coulda been bad,

How it works out is this. Legally, if you have flame arrestors, OK to run 'em either way. Without flame arrestors, they HAVE to be faced away from the engine compartment on open engine boats. Closed engine compartments, you have no choice, they gotta be there.
In practice, Circle Racing boats run 'em that way because theres a LOT of water spraying around everywhere, at least that's what I think. Drag racers don't have this issue, really.
FWIW, my honest opninion is that while it takes around 10-15 HP difference to feel it "seat-of-the-pants" in a street or drag car, with NO OTHER CHANGES, it would take at least a 50 HP difference to feel it in these jet boats. You're not gonna see that with which direction the scoop is pointed.........
Ray