I was reminded of this blog entry: http://splinedoctors.com/2008/06/get-down-to-the-root-of-things/
And another I can't remember the location of that talked about the reason for messy head arcs is often the result of root/torso problems.
I find myself encountering this as we speak. In trying to polish up a shot, I had a few people mention that things were a little weightless in parts, so, I went back and did a cursory "re-do" of the hips/torso, and then started in with the head. I then found myself, when trying for nice clean arcs for the face REALLY "fix." the arc of the head.
Reminded of the above posts, I then got rid of all the head/neck keys, to see exactly how smooth it looked, just being on the torso, and discovered how atrocious the hips/torso really was. The cleaner I am getting the hips/torso, not only is the weight better natually, but the head starts "falling into place."
Any one else encounter anything like this, or have any thoughts.
Discovering this weakness really makes me feel like I need to do a couple walk cycles and weight shift exercises, as I often am less then impressed with the weight of the hips in stuff I see online, but am now finding myself doubting I could do any better.