I missed this thread somehow!
Certainly 10mm of slop in RA would explain the poor model!!! And it's a very poor model for a PME! Hopefully this is just a spring plunger adjustment on RA. BTW, sigma values in a good model should all be under 10. Sigma for the MA and ME terms should be less than 5 or so to use them reliably to set polar alignment. Usually the only way of doing this is to add harmonic terms until your RMS and PSD stops improving (or improves less than 10%).
Cheers, Marcus
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