Interesting
with my fingers parallel, almost touching, keeping the whole right hand flat on the table top:
I can raise my first finger to a point where its tip is about 50mm above the surface, without provoking any movement in other fingers.
I can do exactly the same with my middle finger, again, without any effect on other fingers.
I can raise the third finger tip independently to maybe 20mm without the second finger moving, but if I allow the second finger to lift along with the third, then the tip of the third finger can rise a bit more - to perhaps 35mm.
I can lift the fourth finger as high as the first - 50mm - without any effect on other fingers.
So I suppose that bears out George's main point in my case at least.
It might be worth adding that although I play box right-handed like most other people, I've played stringed instruments left handed for nearly 50 years so my right hand has been doing a lot of (fairly) accurate and demanding fretting for decades. I'm not sure it makes any difference.
I'm a "use two fingers, three when necessary" sort of box player. I still don't fancy using my little finger, although I suppose from this evidence I should have a shot at using fingers 1,2 and 4, leaving the 3rd redundant in the way I presently dispense with the use of the 4th.
I suspect the 3rd will get in the way.