Whilst I have added extra tone to the mouth and teeth, the shadow section of the face and the dark underpainting to sections of the coat, I was not feeling that the portrait itself was as close a resemblance as it should be.
I pinned it down to the shape of the cheek and chin and so, I adjusted the profile in this area. It will still need a little refinement when dry but I am much happier with the adjusted profile. The lower picture is the original and the upper one the adjusted one.
I think that part of the problem in seeing this is the fact that, although it is a portrait, it is not a conventional upright pose. Note to self: rotate the painting occasionally to view the image in a conventional upright pose.