Regarding the reflectance of the 'regular' TIE's panels, being the Koolshade was made of tiny black finished metal slats, it might be a bit tricky to get that same sort of effect with the Vader and Interceptor TIEs since they didn't use Koolshade but apparently some form of lighting diffuser sheet with an 'egg crate' texture. I was considering painting the black portions matte followed by an over coat of semi-gloss clear, or even gloss, so it also would reflect light at those angles where the flat surfaces would bounce the light.
This past weekend, I saw two of the AMT 'Studio Series' TIEs at the Northern Virginia Open (NOVA) contest and I could see where the kit tooling replicated the slight irregularities of the original Koolshade very well, giving that same 'patchy' reflectance of the original. I don't know if they were done by RPF'ers such we'd have access to a build log posting, but it would be nice to confirm how they painted the black portions.
Cheers! Robert