First, please confirm your PS1 cable is indeed a PS1 cable (not PS2…there is a difference). The SCART head should have these capacitors on it: https://www.retrogamingcables.co.uk/image/cache/catalog/playstation%20pcba%20left-1000×1000.jpg
I’ll post my PS1 profile settings when I get back in front of my OSSC tonight, but a couple things that come immediately to mind, to try tweaking:
Video In Proc. -> LPF
Try the various options, to see if any one of them dials it in. 9mhz or auto should be the best, but it doesn’t hurt to try them all.
Sampling opt. -> Sampling phase
It’s a lot easier to dial this in with a 240p test suite. There is one for the ps1, but I haven’t used it and it’s not immediately clear to me if you simply burn the .bin file in the resources folder to a CD and run the CD, or if there’s some greater effort required: https://github.com/filipalac/240pTestSuite-PS1
Your PS1 would also presumably need to be able to run back disks.
Failing that, get to a static screen with lots of color, objects, etc, that will let you eyeball the effects of adjusting this setting.
If someone has experience with the PS1 test suite, I’d be interested to know how to get it to work.