Rotating the aperture.png 90° only affects the shadow_mask texture and not the scanlines in HLSL D3D post-processing settings. Hopefully it will be possible in the future so that we can define it in vertical.ini.
Horizontal scanlines on a vertically oriented games looks much better in my opinion and our brains can fill the gaps more easily & smoother compared to vertical scanlines when it comes to moving images.
I'm 100% sure that if true vertical monitors with normal horizontal scanlines existed during the arcade golden age then the developers would've indeed used them for their games instead of just flipping a 4:3 monitor.
“Anyone who has never made a mistake has never tried anything new.” --Albert Einstein