First surmising was correct, the strap goes over my left shoulder, wrapping around to nearly in front of me, and buttons in via Dunlop Straplock
(TM) at the inside of the belly-curve. The further-up location of attachment pulls the whole instrument to the right, bringing the headstock/nut/lower playing positions closer to my center. This means my left hand doesn't have to extend so far to reach them. I have a small tendon issue in my left arm, and this totally alleviates it.
This new strap position also brings the tail end of the bass way past me on my right, pronounced in this case more so because of the length of this design. It's a little extreme, but it works for me- it makes playing so enjoyable, to not be dealing with ergonomic weirdness.
Re-pic:
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Ok those last three are backwards. I am not a regular selfie-taker, but you get the idea.