Parkinsonsniper, you described the technique I use to sharpen my images.
The only diference is I due the masking first, in your girlfriends image I would look for the background at 100%, press ALT (I use a PC) and slide mask until I see no fragments being sharpened, than I would zoom at her eyes....and get lost forever!
Now, seriously, for this image I would take it with f8, so you wont need much sharpening at all, maybe none, which is the whole point of this thread, you rarely need more than f11 in an APS-C.
To be honest with you I never touch the radius slider, when I do its usually because there is nothing I can do about the image, too fuzzy, too out of focus, than I start downsampling it to see if I can still get something sharp above 3Mpixels.
...then our ways are totally different. My way of sharpening is strictly build on the radius slider. Try it and you will see the difference. I wasn't using those sliders, either. Just because I didn't know what they are. Then I said "if Adobe put these here, I think they want us to use them!" LOL
why? they will look at 8:1 zoom on our images to see if radius is ok :))
Serious now. Scenic versus Faces settings. Scenic Preset in Lightroom have this settings: Sharpening amount: 40, Radius: 0.8, Detail: 35. And Sharpen Faces Preset: Sharpening amount: 35, Radius: 1.4, Detail: 15. Can you conclude this?
Ok, I expressed myself too strongly, I try to use the amount slider first, than I use the radius last, its just because it add halos if overdone. If you are not closing down too much the aperture you normally dont need to touch the radius.
Smaller radius value sharpens smaller parts of the image. A scenic photo (a landscape or cityscape whatever) have very small details like leaves, branches, waves, window corners etc. so the radius is lower and detail is higher.
On the other hand, portrait photography needs smoother skins so "detail" is much lower for less skin texture and radius is bigger for adding sharpness to the bigger parts (face edges, eyes, eyelashes etc)
In conclusion, we are not portrait photographers; we need both skin texture and hair lines and eyes and eyelashes....everything we can get out of the photo. I don't think using presets will do any good for us. Every photograph needs it's own settings.