Screen Res and correct aspect Ratio?

[SEE]

My monitor (Native 1080pi) supports a wide range of lower resolutions but virtually all of the others result in an incorrect aspect ratio - Instrument dials are oval and the picture is a stretched 4:3 rather than a true widescreen.

The conf file has a setting Saveaspect= but entering a 1 or 0 makes no difference. Am I missing something as many of the folks I talk to on MP use a wide range of non native resolutions and still maintain the correct aspect ratio?