Thanks for the clarification.
Chances are the technique Nathan deploys is an extreme variation of the "open armpit" doctrine. As you are aware opening the armpit necessitates a higher elbow and vice-versa.
An instantiation of this is seen in the techique of our "graceful friend." He opens the armpiit, engages the blades and initiates recovery. We all know to maximize energy output, the force and required direction of motion must be aligned as much as possible. Consequently, while in recovery his palms face outwards, until entry-point where he penetrates with the first 2 or 3 fingers from his thumb. You can see his elbow is right sbove his back at the onset. I feel this plays a role in how he can accomplish feats like 25 metres in 10 strokes at that height, give or take his wingspan endowment.
Again it is my opinion, Nathan adopts the same principle in overdrive, with his palm facing outward and achieving entry with his thumb all the way down.
I had researched and not found any satisfactory explanation for opening the armpit wrt propulsion. But for now I believe both techniques use shoulder blade as mechanisms to sort of sling the arms.
I have incorporated the open-armpit into my recovery. I believe I have noticed some propulsion boost. But I wait for the summer to be over and resume swimming in my regular 25 yard pool. I can test my SPL there and confirm.
Stillness is the greatest revelation.
-- Lao Tzu
The light of the body is the eye.
-- J. Ch__st.