I like full pillows so typically make them to finish at the size of the pillow form. Since I typically use zippers on the back I'm not sure if it would be different for an envelope style back. Also, I don't care for pillows with pointy corners that are empty so lately I have tapered the corners in by 1/2 inch, starting approximately 5 inches from the corner. Works great for me and I'm much happier with the corners.