Would this hingepin not be bottomed out at or near low point rather than 'precisely between the feet'?
I have always viewed this swing center being slightly left of center...
In every Golf Stroke, there is a Pivot Center (even when the Pivot is zeroed) and an Arm Swing Center. Respectively, these are the Head (or, if preferred, the 'Point-between-the-Shoulders') and the Left Shoulder.
The Pivot Center lies between the feet. The Low Point (of the Arm Swing) lies opposite the Left Shoulder.