looking for advice to mitigate inner groove distortion

Cleeds, I don’t think we are listening to each other. I am saying that I do not think that the particular symptom reported by the OP is due to misalignment. I did not say that misalignment could not cause distortion, although I have my private doubts about the audibility of such distortion. You say that misalignment can be detected on a distortion analyzer. Do you know of any published data to that effect? I would be interested to read any article about that, but I have been unable to find such an article after doing a computer search. By the way, all three of the popular alignment algorithms result in some degree of tracking angle error at the inner grooves, as you probably know. Of the three, the innermost null point for the Stevenson alignment is closest to the spindle. For that reason inner groove distortion with the Stevenson alignment is probably not worse or significantly worse than that of any of the others.But this is a minor point. I agree with you that most of us have made a tiny error here and there in aligning our cartridges. That means nearly none of us is listening to a perfectly aligned cartridge.

I think that the OP might be experiencing an effect of the Rega motor on his cartridge due to EMI. The fact that it gets worse as the cartridge approaches the spindle is consistent with that, just as it is consistent with inner groove distortion. Furthermore, it seems to me that I recall that Rega motors are known to interfere with some cartridges, in particular Grado cartridges, as I recall. But I could be wrong. Checking out the role of the motor in this phenomenon is actually easier than checking tonearm alignment.

IME, inner groove distortion can be caused by many things.  Not sure how old your cartridge is, could be the suspension is worn and you need a new cartridge, or in your case a stylus replacement.  Could be the way the diamond is cut does not like your stevenson alignment.  Try a new stylus. 

Apparently the OP is on vacation.
tz, You have successfully come up with an explanation for the OP’s problem that is even more unlikely or far-fetched than my own or any of the others. Are there any data suggesting that stylus shape and alignment algorithm are linked in any way? If so, I am willing and anxious to learn about it.

Well now lewm don't be so hasty. He also said it could be the suspension. He already gave it an alignment. Maybe just needs new shocks?

IME, which is many years BTW, certain cartridges and stylus profiles do track different and better than others. YMMv but that is my experience.  Not far fetched, just my experience.  my Pickering tracks better than my Grace or my Benz's.  Could be the suspension, compliance or stylus profiles do have something to do with it and I am not sure what kind of QC some of these manufacturers have regarding diamonds and the quality of them.