Well that was an interesting exercise in frustration but I think I learnt something!
After going through nearly every 360 setting for almost an hour and using some internet resources, I am confident I finally managed to work out how you did this with so few filters and the slightly rounded end on the line. But the way I achieved this (and I have to assume it is something close to your method) means that on certain backgrounds with certain circle colours, there is a definite halo effect. Adding unpremultiply alpha helps a lot with that, but slightly diminishes the crispness of the lines. There may well be some setting I’m missing that can help with this (and that will annoy me given the time I spent on that stupid equirectile dysfunction setting) so I await with baited breath!
No unpremultiply:
With unpremultiply:
Reviewing them all again including my first effort, I have re-evaluated and actually like that last one the best.