[12 piece bucket]

D . . . not sure address posture really plays a role here in determining plane angle as far as the "reference point" . . . you can have different amounts of waist bend and still have the different plane angle reference points. Also it depends on if the arms go to End or Top. The other piece is the Shoulder Turn component and its relation to Plane Angle component. Turned Shoulder Plane is generally based on a Flat Backstroke Shoulder Turn . .. but you can get to the Turned Shoulder Plane with other Shoulder Turn components . . . but the book says FLAT. The flatter planes are generally going to have steeper shoulder turns.