The tests i made back in 2013 show some differences between the left and right side airflow patterns in the wing area, when power is applied.
The image for the left side is mirrored so we can spot the differences easier:


When the power is off, the airflow seems perfectly symmetrical:


To confuse things further, the plane in the images above always pulls to the right during pulls and pushes. The vertical lines were perfectly straight but it always needed left rudder to correct the loop segments, proportional to the amount of elevator used. The deviation is pure yaw, no rolling is involved.
I tried everything: adjusting the incidences, wingtip weights, changing the elevator servos, adjusting the elevator throws, etc. None of these worked, so in the end i used an elevator to rudder point mix. It took a few flights to set the mix points properly, but i was very happy with the result.