Insulating the South wall before back filling

Sorry, I am a little weak on pictures for this post but I all that I did was glue two layers of extruded foam to the surface bonded wall. I then clamped it in place and waited for it to dry. I opted to only insulate down 4 feet. Most everyone told me I only needed 2 inches of foam. That would have given me an "R" value of 10. I wanted to be higher than that so the whole house is done with 4 inches of foam, giving  us an R-20. I also staggered the joints, overlapping them 4 feet.