The overscan core option (I used 30 to be consistent with how things looked in Mednafen) did the trick, thanks for that, I wouldn’t have thought to do that.
I didn’t change the ss.correct value in mednafen-09x.cfg, it’s still set to 1… I can’t say for certain how it’s supposed to look, because unfortunately, I sold my Saturn a year and a half ago, and can’t test it.
It’s a little strange if that is how it was though (I honestly don’t remember). Why would they design a console that can’t output video to fill up the whole screen? But then again, why did Sega do a lot of things.
At any rate, between this, and the pressure sensitive buttons now working, it looks like I have no excuse to not use the RetroArch core anymore, and I thank you for that.