There isn't a wrong size. I usually do the 2 1/2. My open space is usually 8" (but can be wider). My left hanging piece is 6". My right flap is 5". I keep a sm sample to help remind me of what to do.
My left piece lays open with right side facing up. Then my right piece is wrong side up with the upper piece laying ontop of the left but forming an upside down L. Hard to describe without a pic.
There are many tutorials showing this with pics. HTH
Last edited by EmbQuilt; 12-22-2011 at 08:36 PM.