[Par71]

Why should impact be before Full Extension of Primary Lever (full uncock)? At that time (impact), PA2 wouldn't matter anyway coz it's PA3 that matters (PA2 power being transferred to clubhead by PA3)?

That’s the Law of the Flail (2-K). The Clubhead is accelerating (Centrifugal Acceleration) until it becomes in line with the Left Arm (Full Extension). Then it settles into Centrifugal Momentum.

Accumulator #2 provides the Downward Motion for your Three Dimensional Impact (2-C-0).

But you are free to execute Impact during Full Extension (with an Uncocked Left Wrist). Homer said that "produces a 'soft' Impact and is very useful simplification" (2-P).