I don't think this conversation is helping answer any questions.
From basic common sense
Sometimes 'basic common sense' can lead you in the wrong direction. I've seen it many times. I don't disagree with what you're saying, however, I don't see definitive evidence either way. I think your definition of 'definitive evidence' is different than mine. Try and find a scientific report that has 'basic common sense' written somewhere in it.
Well, you certainly haven't proved this one:
so far it seems that a reduced back pressure at altitude is the only reason for the increased power or lower MAP required? It seems then that the JAA book is wrong on that matter?
I put question marks there for a reason.