Just to keep the dialogue going and as food for thought, here's a picture from an old textbook. It shows the propwash effect on a twin engine airplane. Though I'm far from being able to criticize the statements on propwash effects on the vertical tail of models or even free-flight models, I know some propwash effect on real airplanes.

The picture draws attention to the fact that this effect or at least an important part of it is not caused by the vertical tail. The propeller's slipstream may be seen as a gyro that is deflected downward by the lift-producing wing. This makes for a precession and the sideward force on the airplane.

On the other hand, pattern models don't use flaps and are set up with zero-zero incidence and zero downthrust. The described effect has to be quite small on a ship from the 'golden era' because it flies fast at a small lift coefficient. (The wing downwash angle and thus the slipstream precession depends on lift coefficient.) But it is still there because some rudder is needed to avoid deviations in upgoing (high-lift) parts of maneuvers. The older models from the early 1960s clearly show the effect because they have a semi-symmetrical airfoil and some decalage and are flying slower.

Still I wouldn't rule out the other part of the propwash effect, that acting on the vertical tail. I could fancy a connection to the propeller's diameter/pitch, rpm, and efficiency. Ballistic models had a small high-rpm prop with bad efficiency, meaning a fast-turning but small-diameter slipstream. Maybe it's gyro effect is small but it's aerodynamic effect on the tail is big, at least compared to later models with a big low-rpm prop. Maybe even the gyro effect is actually small due to the speed of the ballistic models while the aerodynamic effect is still there. After all many models have some right thrust even for the vertical part of patterns.

Anyway, when researching the Brushfire (here on RCU) I found out that 0-0 setting is recommended. That's probably because the vertical tail of this model is nearly symmetric (above and below the centerline). On the other hand, also Phil Kraft had 0-0 on his models with a quite high located vertical tail. I would agree with him and Ed Cregger, use zero-zero setup and get used to the natural behavior of the airplane. At least that's what I'm trying to do.