Yes. Lift Vs rpm convergence shows the effect of viscosity decrease. But not surely. - Maybe heating was very minor over the test. - A convergence proportional to lift is also to be expected and that may be ALL it is.
Welcome. Note I must have edited as you answered. There are two contributing explanations. For all I know you could have worked the tractor beforehand. In which case, cooling oil would have had some offsetting effect on convergence that was strictly proportionate to the lift figure. . . . Or in the case of warming the convergence effect would have been accentuated.Thanks for pointing that out. I hadn't noticed that before.