Wide Open?
 

With professional lens, to back focus properly, you want to open the lens full wide with the iris. Does the EX do this as part of the routine described? If not, you might want to do this before running the program.

If you back focus at say, F/8, you could be in for a nasty surprise when you go to shoot wide open. Give it a try.

Wayne Orr, SOC

of course I always did the adjustment with wide open aperture.
thanks,
Gerald