It's not that easy, I can tell you. Each bit is 2 pixels large and moving them even 1 pixel left or right can make everything look bad.
EDIT: I have checked it, and I don't think I can make it any better. If I move the north-east border, I will have to move the south-east border too (so that they still work together well) and then you would get an overlap in the south-east corners. This file is tricky because of the "3d" shadow under the border, and also because you cannot use a perfect diamond shape but have to distord it a bit to make it work (earlier version was more diamond-shaped but didn't work because of this).