Off-kilter in the best way. One large square pillow with a smaller, rectangular pillow arranged on one side of the sofa with another large square pillow opposite. Asymmetrical but balanced.
Here, repeat your pairing of a large square pillow plus a small rectangular or square pillow on both sides. Up the ante by creating a focal point in the middle of your sofa with one pillow floating in the center.
Button things up with two big square pillows in the center of the sofa with a small pillow in front for maximum crispness.