5d III portrait focusing technique?

If you focus with the center point and then recompose, you'll end up with back focus.

The best thing you can do is to use a single AF point and then aim with spot-AF directly on one iris:



With some lenses like the 85mm f1.2 the DOF is extremely small. Sometimes if you just focus on an eye, the camera focusses on the eyelashes and the iris is out of focus. I. e. here:



Watch in full resolution. You can see the iris out of focus.