When I render, I have a specific x,y ratio (for printing A3/4) that does not relate to the screen aspect ratio. When I render from a normal Perspective view, the screen's X is maintained and it is "grown" in the Y to accommodate the predetermined exported ratio. However when I render from an Orthagraphic view, the screen's Y is maintained and it is "cropped" in the X.
(The 'safe frame' does show this, but it should be consistent no matter the view mode.)