[Jeff]

It is true that if one bends the wrist excessively (either palmar flexion or dorsiflexion) that it will markedly limit the amount of cocking simultaneously possible, and the reason is that the two movements both involve the radio-carpal joint, and ulnar/radial directional movements at that joint will be limited when the radio-carpal joint is not in a neutral position (especially if the joint is dorsiflexed - bent backwards).

Jeff.