Quick question - If you hit with the top 2 knuckles with a vertical fist, how would you be hitting flush? Because the index knuckle isn't aligned with the forearm. With a vertical fist, instead of using the bottom 2, wouldn't you use the bottom 3 knuckles instead?
Vertical fists aren't my favourite tbh. For the simple reasons you mentioned. Bare hand...there's a good chance you'll connect with the bottom 3 knuckles. It's why inverted hooks are my favourite 👍