The good news is that all of the problems you've seen in 1mm thick filters were eliminated with the newest astronomk line.
Bill is using these filters with his epsilon and shared a recent ic1396 image he made. I'd challenge anyone to find anything deficient in the data that is filter related.
He also shared a broadband image made with these newer astronomik filters and the same scope. Again, no filter artifacts.
Sorry for the tangent.
Ultimately it was to make the point that for a 1mm thick filter you only need to add 0.33 mm of additional spacing.