Thanks for the explanation Steo, appreciate it.
Interestingly I just picked up an NTSC Neo Geo AES and it doesn’t work with the above settings. I had to change it to 256 v.active as per the OP. Your settings in the linked list above also work. The only problem with this is that it seems to result in an incorrect aspect ratio.
I can modify is slight using h.samplerate, but eventually I lose the picture before I can rectify it fully.
The aspect ratio seems roughly correct in x2 mode, but way off in any combination of x3 mode I use.
By changing the h.samplerate away from the default are we always going to be changing the aspect ratio along with it?