Mike,

Rather than me muddling through an explanation, please read Ron Wisner's writeup on fresnels at this url:

http://www.wisner.com/viewing.htm

as well as Ron's answer to a question by John Flynn dated 8/20/99 on this page:

http://www.wisner.com/archive.htm

I don't know if Arca places fresnels on the lens or eye side of the ground glass, so can't say whether performing tests using that camera would make possible more meaningful results. Even if Arca got the correct side, one must also confirm a groundglass matt surface 0.190" backset. Otherwise, despite not having a curved visual focal surface, one would still be focusing on a plane offset from where the film will (should) be.

Finally, to reiterate an earlier point, there have been (unconfirmed) reports that, unlike double-sheet Readyload holders, the new single-sheet Readyload holder will account for packet thickness at the packet insertion end. This would finally offer the possibility of emulsion location being a uniform 0.190" as opposed to the ramping result with current holders. For a detailed description of the problem, go to:

http://www.cs.berkeley.edu/~qtluong/photography/lf/holders.html#sharpn ess

on Tuan's large format page. I don't think it would be worthwhile for you to do any more rigorous testing until the new holder becomes available in a few months.