[O.B.Left]

I have to see how this works.
Standing up straight and chest high - does that mean that the plane of the RFFW is horizontal and the plane of the LFFW is vertical? That would be 90 degrees.

Id say yes ......assuming your left hand grip is not Turned. In the 10-2-D grip for instance the Plane of the Left Wrist Cock and the plane of the Right Wrist Bend would both be "horizontal" as you put it. Which has implications to Hand Action as the left hand is already turned to the Inclined Plane at Fix.