@SX720 Thanks for the feedback on the script.
I'm afraid you are experiencing the limitations that exist on the Canon side.
Canon's reporting of distance varies through the focus range, with the greatest granularity at the macro end.
This becomes more apparent in the far field at longer focal lengths.
This is why I recommend the script is best suited as a script for wide angle lenses and for focus control/reporting up to the hyperfocal.
Focusing beyond the hyperfocal is really all about setting the infinity blur. For example, focus at 2*H and the infinity blur is half the CoC etc.
BTW you may wish to play around with my focus simulators on my blog at photography.grayheron.net. These are designed to help you visualize focusing and focus bracketing.