DVD allows only two ARs, 16:9 and 4:3.
CxD is converting anything that is wider than 4:3 to 16:9, unless you force it to convert 4:3.
Converting to 16:9 preservers original screen width in most cases, but there will be black bars on top and bottom of screen.
Converting to 4:3 will fill 4:3 TV screen but sides of movie will be cut off.
There is nothing you can do to make it fit better, if you adjust AR manually you just distort picture.