RE: Three fingers under or split-finger method?
Primarily, the finger method used may be more about what is more comfortable to the individual shooter than an accuracy issue.
It has been awhile, but I do recall that the primary reason given by the guy (coach) who promoted the "3-finger under" method back when I started was, (paraphrased) "You are already introducing problems by holding the bow and putting your fingers on the string, why compound the problems by putting your fingers on and around the arrow?" Made sense to me.