phd,
In that case, I misunderstood you, and I don't think you were wrong - I'm sorry. (I'd interpreted your post to mean that you'd both log P1.)
If I were in that position, I think I would expect the pilot who was familiar with the aircraft to be P1, and I wouldn't log. After all, he's the person who's going to be responsible for getting us out of trouble if I screw up. Just two different ways of looking at it. But I think that, as long as you agree between you, before the flight, who is P1, either method is correct, as long as only one of you is logging P1 at any one time.
FFF
--------------