Though apparently not something I posses :)
After some great critique over on Blab, and everyone agreeing with my diagnosis, I have started playing with his head.
I went back to my reference photos, and re measured, I thankfully found out that his head is actually the right length, but his eyes are too low down, which gives the impression of a shortened head.
But before I made a cut or smooshed anything, I took a cast of his head using silicone putty (which I bought by mistake years ago) and Apoxie sculpt. I am now much happier with the idea of jumping in and messing around.