behind back foot 2:01min
Personally on the flip my front foot pivots out, and remains only slightly south, of the front strap, and the rear then shoots up towards the mast-foot.
I find keeping forward keeps the nose weighted (or more accurately, the mid part of the rail carving) which helps in chop and maintaining speed.
But there's many ways to skin a cat. I see those lads doing a fine job; and they're stepping a lot further back than me, but I'd suspect if you're not got full speed coming in you'd end up dragging the tail through the turn.
Trousers,
Your foot placement sounds very similar to mine. So when I start my gybe, I am fully planing, as I then take both feet out of the straps on a reach or broad reach depending on wind strength, unhook from harness, then I place my forward foot in the middle of the board, in front of the front footstraps and my rear foot is on the inside rail and I then carve the board hard. At this point in the gybe, most of all the leverage has already been applied when sending the board in a carving mode. Now both feet are parallel to each other, perpendicular to the length of the board. As I start to flip the sail, my forward foot pivots outward and my back foot pivots inward following the motion of my front foot. Then my front foot moves to where my back foot was and my back foot moves to where my front foot was. Then I flip the sail when exiting the gybe.
I don't leave my forward foot in the strap for the first half of the gybe because it puts too much twist on my knees. Less leverage with the front foot out of the strap, but it saves my knees. I can visualize a potential ACL injury with my forward foot in the forward foot strap pointed outward and my knee is pointing more inward for the direction I'm leaning into the gybe. In essence, that position seems like how a side blow to the knee would occur. Your front foot is locked in the forward foot strap pointed outward and your front knee is forced to turn more inward with all your weight and leverage pushing hard towards the sail on that forward knee. I get the chills thinking about it.
I do envy those who gybe with the forward foot in the forward footstrap. That's the best way to get the ultimate leverage out of the gybe. With both feet out of the straps, there's no way to do a laydown gybe. But I can do a pretty nice planing carve gybe with both feet out of the straps. It definitely takes more out of my arms, but I'd rather have strong arms than an ACL injury and be out of commission for a season.