Some interesting ideas for 'field trials' here! ('Excuse me, madam, I need to assess your ability to wear high heels; I have a tape measure ...' )
The suggestion that, regardless of flexibility, a 3" heel is as high as one should go defeats the object of the exercise somewhat. But I can see that the warning of bad posture, back pain etc is well meant - although many people find wearing heels alleviates lower back pain.
But I do agree with this comment: "Heel position is also vital. The heel of the shoe ought to be directly under the heel bone for maximum stability. ‘Lots of designers mess around and put it too far back on the shoe,’ says Emma. ‘This means you’re striking down too far back on the heel every time you walk. It’s one way to break the heel of the shoe and send you tumbling.’"
Very few of the readers' comments (230+ so far) have any substance; the majority are the usual anti-heels condemnations from those who lack either experience or tolerance.