What you say is very true and certainly would apply if the focus was slightly off at the wide open aperture and there was 'NO' focus shift. The added DOF would probably completely mitigate the mis-focus. However with the shift I am experiencing the DOF is increased but shifted behind the lens and, of course, also in front - but not enough to make my target sharp.That is quite weird, because usually the nearer your target is, the shallower the DOF. I would rather assume that with objects standing further away the DOF would be greater and thus focus errors more forgiving.
Victor