[Yoda]

Using my dowel, I applied extensor force , which puts pressure on my right thumb pad onto the top of the left thumb, which stretches/straightens the left arm. I get that. Also causes the left wrist to flatten and cock, and the right wrist to flatten.

GolfCatty,

With the Left Wrist in its Flat, Level and Vertical Impact alignment, the correctly applied 'Stretch Below Plane' Extensor Action (through either the #1 or #3 Pressure Point) should never cause the Left Wrist to Cock nor the Right Wrist to Flatten. In fact, to the extent the Left Wrist is Cocked and the Right Wrist is Flat at Fix, the opposite should be the case.

Remember, the whole idea is to assure structural rigidity -- to get the 'wobble' out of the Power Package -- by stretching the Left Arm (and ideally the Clubshaft) into a straight line -- the Plane of the Left Wristcock Motion, a.k.a. the Plane of the Left Arm Flying Wedge. Try again.