Long time no see @Tromzy! I’m glad you’re having a good time with your customizations!
@HyperspaceMadness has been talking about the anti-aliasing effect this setting can have for quite some time now. Once you like the results you’re seeing, I’m happy.
There was a time when my presets probably had that setting at 100 or 200, that was back in the rolling scanlines days (but that was before the recent changes to the blur behaviour and strength). I’m now very sensitive to blur though so I’m very cautious about its use particularly in older 8 and 16-bit era games. If there’s too much blur, things appear out of focus for me, especially at close distances and that can wreak havoc on my eyes.
Have you tried setting the setting above it to 200? Also, you can add blur in a different way (I think it works and looks differently) by lowering the Signal Resolution in GTU settings. There are 3 settings to use. The 1st affects the resolution and sharpness of the image itself, while the other 2 seem to affect the colour resolution and can cause the colours to blend into each other more to create an NTSC Composite effect.
Have you tried my new Arcade - Sharp, Arcade - Raw, Composite - Pure and Composite - Sharp presets yet? Just by using those alone, you should see a reduction in aliasing due to the mask and scanlines settings.