you are rigth, the 12" against a 10" EL tonearm in reality makes almost insignificant " improve " in tracking error. Using Löfgren A alignment IEC:
for someone who insists on 0.1dB riaa accuracy for hi-fi, you sure seem to have a very loose definition of the word "significant"
All those with 100% accuracy in the alignment but any tiny inaccuracy in the alignment makes that the 12" error gone way higher than in a short tonearm.
I believe you have gotten that backwards. The shorter the arm, the quicker things get ugly with any misalignment. This is assuming an advanced profile that has a very small window of "acceptable" angular error to begin with.
I guess this thread is about a cartridge with a conical profile but that doesn't change the general pattern of behavior.
and finally.....
Maximum distortion difference between null points is only 0.1% if alignment accuracy is 100%: zero tolerance.
I do not believe the "weighted" distortion measurements derived from the formulas is actually representative of the sonic penalty angular mistracking error can cause. It may serve as a great technical cudjoe to beat people with but I generally trust arguments formulated from the listening chair rather than from behind a computer screen.
dave