Corners

I don't quite understand the shape of the corners in Stroble's drawings. He does mention they are drawn from his templates and hence the lines are meant to be cut out. The dashed lines showing the outside surface of the ribs converge and I cannot figure out how to make them join within the drawn corner of the front and back. My corner is little different from the drawing. It was my attempt to make the ribs join over a shorter distance. I don't like the look of the corner now. I will make it shorter but I am not sure quite how to get nice looking curves. I suppose I should have thought about this more before glueing the ribs.