I am curious to know. When you make your binding 2.5 inches, what size seam allowance do you use to attach the binding in order to have the binding full? If you use 1/4" it seems that the binding would not be full. 2.5" folded in half is 1.25". Then 1.25" - .25" seam = 1". Then when folded over the quilt it would be 1/2 " if it was folded equally. But it would only be filled by the 1/4" seam allowance.
Do you leave your batting/backing wider than quilt front? Take a bigger seam allowance?