Your hand position can be varied clockwise or anticlockwise from the photos you posted, or maybe I should say wrist?
Anyhow the way that you have the sling attached is similar to myself, I have it cinched on the base of my finger not as high as yours. Alternate your hand , palm left, right, down, up, they all change the throw. I can put heaps of backspin on spheres with the right throw and hand positions, the cinching fingerloop allows fine adjustments.
Just as you noticed the grip width changes things so does the retention loop.
Personally I feel the “90 degrees “ allows more freedom of movement while keeping the cords parallel.

So, I have always done better with slim and trim slings.
That's why mine is tapered. That being said, my best functioning sling is still just a semi split leather pouch with paracord cords.
I find the leather slings really depend on the leather itself.
Not only does one need a long cow but the thickness and pliability come into play a lot.
You'd think you want a nice soft whippy sling Mersa but it would wear out and stretch pretty quick. What I do is take thicker leather and then break it in by hand crosswise if you will.
This allows the sling to bend and lag easily but still stay flat and perpendicular to the path your arm travels.
I think Jaegoor first put me onto that idea of side bend on slings when he was doing a tutorial on 5 vs 7 vs 9 strand braids.... Some years ago now if my memory serves!

Hmmmmmmmm
Although I do sell them I would also be open to a trade.
Hit me in the DMs whoever's interested.

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