Sorry for the belated answer:
It’s tough to give advice regarding the PS2. PS2 games use different internal resolutions and it’s a pain trying to achieve correct aspect ratio. I have spent a lot of time fighting squished aspect ratio, especially 480i games. There’s no easy fix. Sometimes it works adjusting H.active to 704, 686 or 640. Sometimes even as low as 512. Aspect ratio is unfortunately one of the few areas where the OSSC is hard to work with and one I hope will see an improvement in the new hardware revision.
480p doubled to 960p on my LG OLED works fine, but I prefer 480p since it has less black bars.