Quite a few of Kim's other "character" pictures are centred on faces too - or, like the Hong Kong uniform one, use the individuality of a face as a foil for the (faceless) uniform or costume.

That's a very good analysis. I think you're right and he centers more like...an aspect of the face...the expression he thinks should encompass the character as he sees it. It's like a snapshot of the character and not the character itself.