This article, written by a banjo player, is full of creative ideas and
solutions. I had never heard of the one of looking at your tendons on
either side of the wrist to find a good arch.
Here is the article:
http://hawthorne.fastie.net/gestaltbanjo/gbv1-7.htm#footnote2
Apparently banjo players believe that stability of the wrist gained by
anchoring 2 fingers (a + c) increases speed and control of im. I
wonder if this technique could be adapted to CG for runs. John Dimick
pointed out the trick that sneaky Yamashita used, of anchoring a on a
string while alternating im.
He also claims that the connection between am fingers is "mostly
mental". That's a new one on me! although he does back it up:
http://hawthorne.fastie.net/gestaltbanjo/gbv1app6.htm