[Yoda]

...confusingly, the 10-5-E Closed Plane Line can be worked into the Swinger's procedure, e.g. to hit a draw.

When you say "cover", you mean visually cover (i.e. from the player's view) don't you? I ask because the plane cannot be so upright that it's vertical to the ground!

The Swinger using 10-5-E to hit a Draw is not the same thing as the Hitter using 10-5-E as the Angle of Approach Delivery Line. The former Traces the Delivery Line -- 'points at it' with the Clubhead -- whereas the latter 'Covers' it (also with the Clubhead). This Covering -- the Clubhead directly above the Delivery Line -- is 'for real' and not merely visual.

Covering does indeed cause the Hitter's Plane to be steeper. However, it does not cause it to be Vertical. Instead, per 2-J-3, its Angle is dictated by the Clubshaft motions required for the Clubhead to cover the Angle of Approach and its extensions (before Impact Point and after Low Point).

The good news is that all Delivery Lines -- whether the true Geometric Plane Line or its Visual Equivalents (Arc and Angle of Approach) are Traced by the Right Forearm and the #3 Pressure Point. So, as always, the discipline is to get your mind out of the Club and into your Hands.