Sorry Stressfree but I have to agree with Moggie.
P1 is the pilot whose sector it is, P2 the other. During the approach when P1 has handed control to P2, P1 is the NHP until he/she takes control again at decision altitude/height.
I think that when written down it might appear complex, but the teaching, implementation and use of the monitored approach method is actually quite simple. Plus it works very well indeed. Very few pilots who use it or who have used it complain about it. It seems to be those who've never tried it who have the most to say.