So I have repeated the focus test using this focus test chart at distances between 24cm and 2m. In summary I think my results are much better than before.
The chart is really only good to about 1.2m as it is too hard to accurately see and focus on the thin vertical lines after that.
One thing I didn't consider when taking the shots (or even when adjusting the height of the viewing screen when calibrating the focus) was to keep the test object perfectly vertical, and the camera perfectly vertical for close up shots (lets say between 24cm and 50cm). When the lens plane is not parallel to the object's plane then the closer you get, the greater the focus error is. I think this is fixed using Mamiya's paramender. Up until now I only thought the paramender provided a vertical offset, but if it provides an offset while keeping the lenses in the same plane (assuming the lens plane isn't vertical) then that would solve this problem. Surely other TLR users have this problem with close up photos if they don't use something like a paramender.
I now want to test focus for distances between 2m and infinity. Picket fences and home made collimator here I come ! Actually did you know that you can make a collimated light source using a 2nd SLR camera ?