I try to keep the concepts of pitch stability and pitch trim in two seperate compartments of my thinking process.

The neutral point is established by the plan of the aircraft and the effectiveness of the flow over the wing and tail. Consider it essentially fixed (with minor exceptions) after the aircraft is built. The static stability is established by where the CG is placed relative to the neutral point. There may be some change in CG location between a full tank and an empty tank. This is accomodated by making the static margin large enough so that, with the CG in the aft most location, the stability is adequate.

The pitch trim is established by balancing all the forces and moments. This is done to establish a trimmed airspeed by adjusting relative angles between the thrust line, the chord line of the wing's mean aerodynamic chord and the horizontal tail chord line. The thrust line is also adjusted for a minimum change in pitch attitude over the throttle range. To make this proceedure practical, two of the three critical angles must be adjustable. Notice that the word incidence isn't involved except possibly as an intermediary between the three functional and critical angular relationships.

By adjusting back and forth between stability and pitch trim the model can be brought near its ideal setup.

Now what's so complicated about that?