This is a good idea. Currently, the head is always at the same angle unless the rider starts to sit up really straight at which point the head starts to rotate back in proportion to the torso angle.

This was all done automatically in an attempt to make the interface as simple as possible. However, I now see that it would be better to give over this control to the user. My inclination would be to add a field for the angle of the head relative to the horizontal rather than the angle of the head relative to the torso. If anyone disagrees, please let me know...