there are three bolts which hold the bracket to the bike.
the lower (front) bolt is where i spaced it down 1/4"
by moving the bracket straight down, there is a gap opened between the rear of the bracket and the frame.
this gap can be filled with roughly half the thickness of the lower spacer (because the rear of the bracket is at roughly a 45 degree angle)
the bracket moves straight down (because the front bolt hole will not allow forward or aft movement) but because of the angle of the frame it must be spaced to fill the gap.
hope this clears it up for you