I don't know of a way to move the line up (or make it go away), so I've generally tweaked the overhang to make it bigger and coincide with the line. If you follow the suggested dimensions for the overhang then it will line up correctly:
viewtopic.php?f=34&t=25476&hilit=maximum+graphic+pixelsAlternatively, if you call EnableOverlay(true) on the dialog the line won't show up at all, but it also won't dim the screen behind the dialog.