I just discovered this and wanted to share. I had no idea how big a component a tight finger loop is in controlling accuracy until now. I had just made a new sling and suddenly my accuracy went out the window(much more than the usual drop from switching between slings).

Turns out it was because the finger loop was very loose on my finger, augmented by the fact that this is a much heavier sling than I'm used to(I did a hemp 9-braid, 70 grams!). After a couple dozen throws I realized it was sliding all around on release and I was subconsciously contracting my fingers to try to pinch it into place which was certainly throwing off alignment, not to mention the sling itself sliding around throwing off alignment. I came inside, tightented the finger loop and went back outside and found my accuracy immediately jumped back up to where I would expect for an unusual sling.

With this in mind I would say this is much more important for heavy slings since their extra weight will make them want to slide off your finger more, but still important for lighter slings since they'll wobble around if they're not tight. I imagine that double finger loop slings have much less of a problem with this than single finger loop, but I don't think the double loop would totally eliminate the problem on its own.

If, like me, you are not great at making slings and you accidentally make the finger loop too large, not to worry! After the fact you can always tighten up the finger loop with a simple stitch around and through the center of the "neck" of the loop to make it the right size for your finger without having to rebraid it or modify the sling in any other way. This will work with nearly any material(unless you're using steel chain!). And you can always easily snip the stitch if you need to make it larger again later for someone else or for a different finger.

I've always gone for quite a loose fingerloop. I started on the ring finger and you don't need that to be snug just because of the angle when you release. Now I've switched to middle and need a little tighter but not too much.

I do think that is a good strategy for shrinking a fingerloop though. You can synch down a too big fingerloop, but you can't make an existing fingerloop bigger.

Good stuff.  I prefer a snug fingerloop.