I don't think the goal is to prove whether spiral propeller slipstream exists or not, but to see what can be done to improve the knife edge behavior and rudder response. Obviously the contra drive offers many advantages, not only removing the need for right thrust.
I am curious though about what causes the need for so much right thrust in our models.

In extreme cases, like full rudder deflection at low speeds, the airflow around the vertical tail separates completely. Rudder still works, but the braking effect from the extra drag is quite visible:



To improve the airflow around the vertical tail, i plan to add 1-2 fin fences, then i will experiment with 15-20mm tall fuselages fences or strakes, which should stop the air leaking from the high pressure side to the low pressure side around the belly pan and turtle deck. It will look a little strange, but probably so did the canalisers when they were first introduced