I checked my GG to lb distance and compared it to the filmholder, and found the holder was 1mm deeper. I figured my back was built for a fresnel between the gg and lens, but wanted to double check here. You measure from the ground/inside part of the glass, right? Just thought I'd ask, thanks,
Yes for the mesure from the inside part of the glass, the part on the side to the lens, and you must have a sheet film in the holder.
If you get 1 mm difference is really too much, you should have the same distance.
Jack East Jr. wrote a nice article about that in May/june 1999 edition of Photo Techniques. It was reprint in "Way Beyond Monochrome" by Ralph W. Lambrecht & Chris Woodhouse.