I'm sorry that you don't get it. P-factor does not exist in straight & level flight. It only exists during maneuvers involving high angles of attack, like climbing. For those of you who don't know what angle of attack is/means, here's the def: Angle of Attack is most frequently defined as the angle between the cord line of the wing, and the relative wind. Generally, it is sufficient to say that the angle of attack is simply the angular difference between where the wing is headed and where it is going. (per FAA's Flight training Handbook). The FAA's Flight training handbook is really good and is written such that an 8th grader can understand it. It can be downloaded from their web site free.

If torque reaction from the engine & propeller, corkscrewing effect of the slipstream, gyroscopic action of the propeller, and asymmetric loading of the propeller (P-factor) was not an issue with our models, there would be no need to do any trimming to them if they were built straight & true. Like it or not, all the trimming that you say you do to your aircraft is to counter the effect of those 4 items.

FYI: I've been building & flying model airplanes for 45 years of my 50 years on this earth. Also, I've been flying full scale for almost 25 years. I'm also an aircraft mechanic. My real job is a mechanical engineer.