First of all - Why don't you want to tell the name of the book?

I can follow your theory, but am pretty sure that the P-factor far outweighs this. Especially in the size plane you are going to fly. Maybe on a big multiengine airplane the factors are more equal.

You said you are a multi engine student. How far are you in the progress? The school/instructors you are using should give you a very detailed education on the particular factors affecting the airplane that you are flying and their effect on Vmc. If that is not the case you need to pick another school.
There are a lot of bad flying schools out there that doesn't teach their students crap - Make sure that isn't the case here.