I ended up finding it easier to just use the Sony Megatron Reshade preset with Retroarch. I didn’t expect it to work so well or look so good. It’s the same config as my PCSX2. I’m not sure how the line count is adjusting, but it’s extremely crisp, and breaking the “pixels” up naturally, so I’m happy with it.
For PPSSPP in retroarch, it’s great because I can do higher internal resolution, which really helps with image fidelity, but then the lower rez sprites naturally sharper look due to the gaps between scanlines, which for the games pictured, make a lot of use of 3d & 2d assets.
I’m far less worried about the “right” way to play psp, and more just about getting a really bright picture w/ scanlines & “phosphor glow” that I’ve had on my Sony Trinitrons I’ve been using lately. As you’ve said, just kind of letting my eyes and personal taste shape the “right” experience for them.
And, I think this pretty much replaces them except maybe for old PC games that were 4:3 ( the glass & native resolution for ~800x600 era games just fits really well on my Sony HMD-A440).
I’m sure this is doing some things “wrong” though, as you mentioned, I’m not explicitly reporting the resolution to the reshade preset. It’s somehow inferring it. I’m sure if I used a addon/preset to handle that I could get the scanlines to look even more accurate(?). But honestly, it’s at a really convenient point where the preset just works for all content, which is kind of the dream (for me at least). So I’ll probably just try actually playing through a few games with this setup for now .