This is normal for this technology. You can minimize it with the service controls available, but you will likely need to do significant realignment to the geometry and convergence. The auto convergence sensors also have to see enough of the image to operate, so minimizing overscan can make it fail to work. Another method is to shim the CRTs or bulkhead to move it closer to the mirror. This also causes you to have to do more realignment and also may use more of the phosphors (if you go too far), so any wear may be obvious at the edges if you begin to use fresh phosphor.