Unable to sharpen selected subjects face

I'm having an issue trying to sharpen just a single subjects selected face in a small group photo.  One of the subjects is falling out of focus and a little soft. I selected the subject and made a mask of just the facial skin, but the sharpening slider is not having any effect at all, even jacked all the way to the right, viewing 100%. All of the other parameters of exposure, etc. show change in the face. I can sharpen the whole photo and see the results, but I just want the change localized. What am I doing wrong?!