I have a new Vizio LCD LED HDTV with a R-15 DirecTV receiver. If I set the screen mode in anything other than normal I get a distorted picture. In the normal mode the picture is less than a full screen. Is the only solution to this problem a HD receiver? I have HD on another TV so the proper dish is available for a HD receiver. Also, will a HD receiver work OK if connected to a round 18" dish?