Super helpful picture, many thanks.
So it looks like the Kipon adapter I am using has a similar length, mount-to-mount, to the Nikon - FX in your picture: around 28-29mm (I am measuring it using a standard school classroom 30cm ruler! So it may not be completely accurate.) So, perhaps it is the Kipon adapter that is the problem; though I am sure I have seen comments here, or on other forums, that say they have no probs with using the Kipon and the FD 50mm 1.4 for the XE-1. I wonder if Kipon does different length FD-FX adapters. It would seem a strange thing to do.
Do you know of any FD-FX adapters that are the correct length and would allow me to focus at infinity?
Again, many thanks for your advice!