This can certainly be thought of differently.
Prehaps it is the lack of mobility in the ankles which ultimately results in forward head posture....and not the other way around.
It is the entire body which passes over the foot with each step.
Failure of the foot to permit this motion will ultimately be met with adjustments within the postural frame.
Is the tightness in the lower back the cause....or the result of trying to resist the forward flexion of the torso and sagittal plane motion is restricted at the foot level?
Howard