Aha! So suddenly the light bulb begins to glow (dimly). So P-Factor is very similar to the effect that limits the top speed of helicopters, that the advancing blade produces more lift than the receding blade. In this case the down stroking side of the rotating propeller?
So even with same direction props the effects are dampened by the thrust spacing from the centreline which with the Whirlwind is also the C of G? Won't this spacing from the centreline affect hard turns and manoeuvres like Wingovers also?
Basically there seems there isn't a huge advantage then to contra-rotating propellers? Apparently not enough to encourage the designers to hand one of the Peregrine engines, which was easily done apparently.
Thank you RTHolmes, that drawing helped a lot!