Originally Posted by Gray Beard

Flywheel, look up the term P-factor, I have a feeling that is what you were thinking about.
Most trainers I have seen these days have the fire wall angled for the thrust as the manufacture decided was needed after a lot of flight testing. When I build a plane I set the thrust at zero and after flight testing/trimming I then decide what is needed, CG, Lateral balancing, incidence and thrust.
With a trainer I usually trim for flight at just a taste over half throttle then make any changes I feel are needed. Engine thrust angle is often the first place I start after balancing but it's often just the balance that needs changing. When it is thrust angle I use washers behind the engine while at the field then when I get home I make up an angled shim to replace the washers.