The lower brace, per TBB, maintains contact with the string longer, transfering energy longer or more of the stored energy from the limb is used, however you look at it. this is deceptive because a few twists of the string, make the pull feel higher, buts its really less efficient.
I try to get to a fistmele, and then see how it shoots. any wristslap? does the fletching clear the riser? go as low as you can without those two problems and you're good right?
I had heard the rule of thumb was the old english width of the stick that it was legal to beat your wife, enforcing "moderate correction".