It really doesn't matter at all which barrel is first! I've seen my coach break 20 out of 25 Skeet targets with the gun behind his head ..at his hip.. or under his arm.
He says if you can shoot you can shoot anything else are excuses!
I also saw him win over 100K at a live bird shoot in Texas..He's good! and likes to play the options. Don't overthink it! For most SC shoots 2 LM chokes and a bunch of 1 1/8 oz. 7.5's will break every target on the course!
I've seen these stunt shooters, and always been sort of amazed, but also wondered why they aren't barred from the range for such behaviour. Safety First of course.
I learned skeet from a fellow that could outshoot me with a .410 but that was one of a matched Skeet set which all weighed and swung the same.
His Skeet Set was Only missing the 28 gauge, lost to his X in a messy divorce.
So he would shoot the .410 in the 28 ga event. Also shot a 20 in the 12 ga event sometimes to mitigate accumulated recoil.
He called it an Under / Over because he Always fired the lower barrel first. Again for recoil mitigation.
Funny guy, great to have on a squad. He kept everyone loose. Really made it fun, and always scored better. Miss him.