I don't have any VGA captures to work with and i'm going by staring at a CRT running a Voodoo2.
Sadly I don't think I can do a shader to replicate the alpha blending artifacts given the limitations of eFX to be pure postprocessing (rather than allowing to alter blending functions)
I'm not claiming this is accurate at all - it still needs dithering overhauled to look like the dither seen in an unfiltered Voodoo capture, and when it comes to HLSL/CG syntax, i'm still a complete idiot.....
I would post about it on Falconfly (for the learnening of the techniques used) - if registrations were open 😒