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PEC on the PMX seems touchy. I did some PEC on my PMX and at first it did not seem to make any difference like you are experiencing. There is the possibility of course that the East/West is back to front on the data so its told to push when it should pull but that probably isn't it as that would most likely worsen. Although one time I did have that reversed it didn't seem to make a lot of difference.
3 second intervals for the PEC log may cause an issue as you want more frequent samples for an accurate PEC curve. Also keeping the other points in about which spot in the sky you use for your PEC guide star.
Another would be to do the PEC curve on a night of good seeing. I haven't read the instructions for a while but I do seem to recall shorter exposure times being recommended to get a more precise sample. Also about a 20minute run (requires good polar alignment otherwise the guide star drfits out of the imaging box). When you think about it 3 seconds is probably way too long as these corrections in the PEC curve whilst they tend to be smoothed out they still move a fair bit over 3 seconds so you don't want a PEC that is always coming in late or averaged over too long a time so the corrections are always coming in late either too little or too much.
Having said that I doubt that is the reason why you are having trouble as it would still make some difference as the curve is smoothed out a fair bit during the final steps of making one. It sounds like its way off, out of synch and your autoguider is having to correct it for bad PEC adjustments.
But apart from that it may be best to ditch Sky X PEC and use PemPro as no doubt you know the above. Especially being a remote system and you don't have many nights to experiment to find out it was some software bug in the SkyX after several nights of trying.
I used Precision PEC for my PME and that got a nice curve. It was a subtle sine wave which looked much like my PME's PEC curve.
My original PMX curve seemed too much for correction. On the PME its a pretty gentle almost sign wave type PEC.
There were in the past numerous threads about Sky X and PME PEC being out of phase so there is a question mark over it.
When I redid my PEC using Sky X on a night of good seeing with the Polar alignment already very very close (probably not as close as yours is now) I got a very good result.
Another factor of course is how stable are you optics in terms of flexure and mirror shift? Protrack corrects for flexures of various types, PEC of course for gear errors.
Another thing that threw my PMX off at one stage was a bit of dirt or something got on the worm so about every 3 or 4 minutes I would get a bad PE spike that threw the guiding out for a few seconds resulting in double stars in the final image. A replacement worm corrected that. Not sure what the spike was caused by in the end - dirt? Damaged worm from the slipping gear/cam issue? Either way it fixed and I do get a noticeable improvement in my PMX using PEC so it can work even if perhaps a bit touchy.
You are imaging at 3 metres though and I image at 1260mm on my PMX so everything is 3X exaggerated on your setup compared to mine.
On my PME I find a 300 point Tpoint model does improve roundness of stars using Protrack at the same time as PEC on at 3 metres focal length. So Protrack is correcting some minor flexes that are slow to show up in the image. It can be odd as when I watch the guiding some of the corrections are larger than what I would think is ideal yet the images show round stars. That must be the Protrack flex correction being added to the PEC curve correction plus the usual autoguiding corrections if they all coincide in the same direction.
My first action would be to redo the PEC using Sky X and make sure its exactly as per the manual and if still no go then try PemPro or Precision PEC and see how that goes.
There is no spike in your PE curve so PEC ultimately should be pretty easy.
Greg.
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