Why don’t you try Mask 6, which is 3 pixels wide in an RGB Subpixel pattern?
The Mask size would have to be 1.
The Slot Mask Width would match the number of Subpixels across the mask is so 3 or Auto.
Then set a height suitable for 1080p. I’m not sure off hand since I last did this a very long time ago.
After that, adjust your GSL Scanlines type and scaling settimgs to what you would looks right and you’re good to go.
Don’t touch Mask Zoom.
For testing on a 4K screen, disable scaling in your GPU driver and set your desktop resolution to 1080p.
That should turn your 4K display into a smaller 1080p subpixel accurate display temporarily.
Unlike what @Jamirus said above. I adore ~360 TVL masks of any kind. You just have to know how close or how far to sit from the screen but at 1080p, “beggars can’t be choosers.”
(And I can say that without putting down any 1080p screen users out there because I have a few 1080p displays which I love and have tried to make the most of.)
Aperture Grille doesn’t really lose much at 1080p though.
For 1440p you can use Mask 10, width 5, set height to suit. I’m bound to have some examples of that 1080p Slot Mask in action. Will update as soon as I can find it.