To refresh... the following was in answer to why a 4 stroke (longer prop at less rpm) might have exhibited less yaw than a 2 stroke on a given model.
ORIGINAL: UStik
The following might explain that (more air accelerated less and thus rotating less).
Actually, your thought might have another tangent... that more air is compressed less. A prop is an air compressor creating high pressure aft of the prop and low pressure forward. Is it then that the compressed air pocket lies closer to the fuselage and is more compressed with the shorter prop at higher rpms and thus exerts a greater yaw force? Perhaps the yaw has less to do with any spiraling as it does from simple pressure differences.