Regarding the spiral slipstream, I don’t think smaller diameter necessarily gives smaller spiral slip stream? It would if rpm remains constant, the bigger prop stirs more air. But for equivalent power, smaller diameter means smaller amount of air must be affected more vigorously??

Regarding what is the best amount of right thrust to use, Mr. Hanson above is exactly right, there is no magic best answer. By definition a single spinning prop is an asymmetrical confluence of forces. All prop effects change as flight conditions change. There is an optimum configuration for each individual flight condition, but not one for all conditions an aerobatic plane sees. A design parameter such as right thrust can be varied to optimize or "bias" a design for easier handling during a particular condition, but at the expense of more corrective input needed during other conditions. For example, if you personally are good at steering straight during inside and outside loops but are not so good at holding verticals, then more R thrust might be better for you. If you don’t hold heading during inside and outside loops very well but can fly the heck out of verticals, then probably little or no R thrust could improve your own overall performance.

A good pilot will understand the effects involved and therefore understand the control inputs necessary to correct. “Good” of course meaning able to carve out the maneuvers consistently and exactly as requested. The good pilot will understand the design “biases” that have been built into a particular aircraft and then behave accordingly at the controls. A good understanding of what effects dominate during individual maneuvers, and which design variables compensate for which effects, enables a pilot to choose a more optimum set of design "compromises" for flying a particular type of aerobatic sequence.

Multiflyer