If you can focus right, then the face wouldn't be blur, assuming you focused on the face.
I'm rather confused by what you're trying to ask.
Are you saying that you focus as sharp as possible on one point, but that point is not that sharp when viewed on PC magnified?
you shoot a full length shot and expect can see fine details on face? not a lot of camera can do that, try high end cameras.
each lens does have sweet spot, usually it will preform well from corner to corner at this aperture, when you not using the sweet spot, even your subject is in focus, it may sharper at the center of the images, but the outer parameter preform poorer.
I seen some full figure samples from Leaf's medium format sensor. They can get the details you want. Prices for the cam starts at 30k.
Try stopping down to F5.6-1 you'll get the details. Anyway why not post the pic up here for all to see if you have any motion blurring.