I should probably speak again to this, as I may have been a bit shorthand.
Overmodeling means, in the sense I'm using it, forcing too broad a range of too many values into too small a shape. It's forgetting the "big picture". I used to do it routinely in the knee (of a nude model -- how I remember the days, and those knees.) By golly, I'd articulate that patella and those tendons and the adjacent muscles until no movement was possible -- it was a sculpture in marble. It was immobile -- and lifeless. [I was very shy back then about this whole gig, but one day after about the third reference in a critique to "overmodeling", I just blurted out in front of everyone -- most of them already art majors before they'd come to the studio, and I in turn only knew one guy named "Art" and I didn't like him -- I said, "I don't know what you mean by the term 'overmodeling'". What I'm telling you here is what my instructor told me. He was right. (I don't really care much if I am, for anyone but me, but if this is helpful, use it.)]
Don't do that. In any small area, you're not likely to see a full range of values, from darkest to lightest. It's possible, but unlikely. If it happens, be aware that it will create value contrast that will attract the eye of the viewer. Did I want the viewer to notice the knee? (actually, I did, because I was new and wanted the viewer to notice everything I did), and do you want the viewer to first notice the ear? Probably not.
Again, it's the photo. The darks in the reference are too dark (and when you're working in color, they're often colorless), and the lights are too bright and colorless as well.
I also want to go back to that right side (ours) hard-edge issue. That's also a photographic effect (as you've since acknowledged). I want to add here that the "form" problem relates to not just values, but the tendency of hard edges to attract attention and therefore come forward (into our visual attention). A softer edge will recede and thus lend itself to the illusion of form.