I've seen the phrase "as long as you aren't too close" a few times (or variations of it), and neuro mentioned it is most evident at/near MFD.
Which for me kind of begs the question: at what distance to subject would the problem become less of an issue (or a total non issue)? Asking, because I frequently have to change from wide open to about f/4~5.6 with subjects about six feet away (3 or more times MFD). I shoot full frame, if that matters.
In my experience, 6 ft is fine. I can focus with my 5D2 with the outer AF points (!) in AI servo, no problems.