I've seen a couple of respected sources that indicate that the designer of the Remington P51 pistol did some experiments with a large number of people that were something along the line of what I suggested in my post. He then set up the grip angle of his design to be as natural as possible for the "average" person.I like your set-up for that experiment to remove some variables.
I've also heard it alleged that something similar was attempted during the design of the original Glock pistol.
I can't verify the story about the Glock design but here's a (crudely done--my apologies) overlay of a G19 onto a Remington P51 pistol showing that they do have very similar grip angles. (The P51 grip safety is not visible in the picture since it compresses when the gun is in a firing grip and therefore doesn't affect the grip angle.)
There's no change in the relationship of my strong hand/wrist/forearm when I take a two-handed grip vs. a one-handed grip.During all your discussion I had been visualizing everything mentioned with a one hand grip on a handgun.