My 7Pi have the triangular extensions top and bottom per plan. I just never got around to adding the 'dog house roof' rear panels. I have the panels cut and finished, and ready to install. I myself am not sure what value they would add other then additional support. Even then the bottom plate is made up from doubled up 3/4 plywood, and I have cherry trim on top which makes the top plate more rigid then normal. The midhorn needs the extra depth for support.