Actually, that is pretty much how I feel about alliteration in general, and you've put it together quite well in this picture. The constancy of the sound matching the sameness of the name Graves on a gravestone. In your "B" poem, the "b" sounds altogether, the way you placed them, produced a rather explosive feel, and that was perfect. Here, it is the technique of alliteration itself -- at least on one level -- expressing something integral to the scene. And the "gr" sound does seem to call to mind the feel of -- well, it calls to mind the feel of something sharp scratching.