It actually has nothing to do with the tracker model but rather with type of “gaze view mode” you’re using. The default gaze view mode for EyeX is “FreeView” while it’s “ExtendedView” for the 4C. FreeView and ExtendedView are based on two different algorithms and the latter does not support asymmetrical view angles.
The easiest way to only use head tracking would probably be to just turn the gaze sensitivity speed slider down to 0.