I read an article... probably here. A cop talked about learning how to shoot one handed at center mass quickly. I think centered shooting is very unnatural and that is why it requires so much training to not suck under pressure. I therefore spent more than half my time on the range shooting one handed.
Unless we are going to compete or spend thousands of hours training, I think we should shoot the way we would when we pull up our finger gun. (if you are strong enough to control your weapon.) Extend your finger pick a target on the wall and shoot. You naturally turn to the side a bit. You naturally aim with the correct eye and naturally either close and re open or just keep the non sight eye open. I believe your eyes want 2 different lengths so they know how to work together and get a better idea of depth.
2. If you agree with shooting sideways... bringing the other arm up is useful to control recoil or trigger pull but it does interfere a bit with naturalness.
edit... i just found a similar article to the one I read here. I realize he is pushing a different type of shooting but the logic is compelling to me.
https://www.thetruthaboutguns.com/2011/03/john-velt/two-hands-good-one-hand-better-pt-1/
Distance equals time, or lack thereof. If you don’t have the distance/time to assume a “proper” combat stance and grip, you won’t do it. The New York Police Department’s long-term study of thousands of police combat cases confirms it: most officers engaged in an armed confrontation fired with their strong hand. This YouTube video demonstrates the point: