I'm no kind of expert and the theories above make sense, except...
Your bow's limbs are the same length , right?Spaced about equally, above and below the grip?
So, you set the arrow above the center on the shelf , or further above center, on an elevated rest.
Let's assume you pull evenly w/all 3 fingers; Now you further raise the center of your drawing force by putting you index finger higher than the nock (which is already 3/8" above the arrow rest)
If you put three fingers under the arrow, wouldn't you be closer to the middle of the string, and require closer to an equal tiller?
or, ... NOT?
-Hop:confused: