Fascinating discussion!
Alex, are we to assume that there is no disturbance in the airflow on the bottom of the fuselage/rudder? It might be interesting to check there as well. I will be very interested to see the results of the fin and fuselage fences, perhaps you could test them seperately. The placement of the fuselage fences is interesting; they seem to have a very significant positive incidence, do you anticipate trim changes?
The right thrust question seems to have many variables. About 20 years ago I did some extensive empirical testing with a Hanno powered Runaround and discovered that the amount of right thrust needed (for that airplane) varied with the prop (12x11 vs 13x9) and violence of direction change (eg. pull up into a vertical line): less right thrust required for the 13x9 and smoother direction change. Of course, airspeed is probably the real culprit in this case, but the Runaround also has the wing placement very low on the fuselage (far from the C/L). More food for thought...
Lastly, the oil dispersion pattern on the bottom of my venerable MK Topstar powered by a piped, inverted OS 140RX is completely symmetrical. The prop is an APC 18.1x10.