Honestly V4 and PE look even less natural. Heads don't bend back like that unless they're on a pike. There's skin and fat tissue that compress and bulge at the base of the skull and top of the traps bulge a bit as they contract to pull the head back. I think that's what LF's rigging was aiming for.

At any rate, I made this correction morph in about 3 minutes. Setup was another 2.

You can also get a similar result simply by adjusting the right neg bulge map on the head bend to about 0.180 in the joint editor. It's set to 0.10 by default.