Odd behavior with an APAC and pots... ?

[RyoriNoTetsujin]

Hey all, long time no see!

I've had an APAC in use for a while (since... 2015-2016 I think?) in a 2-player cab in all-digital mode (joys and buttons), but I had always intended on using it to create a secondary 360 wheel and/or SW yoke setup with pedals.

Fast forward to today: that cab is gone (lockdownsizing), the yoke is now a no-brainer buy from TSticks (esp. at 30% discount! I also got a push/pull spinner for my Tron panel, which opens up my TurboTwist for a dedicated 360 wheel!), and I'm finally getting around to hacking a set of yard sale Mad Catz PS1 pedals for use with the APAC.

The pedals are running typical 10k pots. I've wired them per Andy's image on Ultimarc. They test good in Windows calibration when wired individually with the APAC, but when run together on the same player side, on either player side, there seems to be some sort of crosstalk/interference/shouldershrug(?) because the raw data in Win calibration jumps all over the place and the sensitivity is way, way off.

I've also tested this with a couple of other 10ks and they exhibit the same behavior. Fine individually, crap together, when installed on the same player side.  So is this the APAC, or something (especially) weird in Windows... ?

Fortunately, the kludge for my situation, running just one pot per Player side, is functional ... but only because I now only need to use two total pots (just the pedals, not the yoke) and I can configure MAME to compensate.

Can anyone illuminate what I'm missing? Or could this be a legit issue with my particular APAC that I just never noticed before? It has been knocked around for some time now...