RVlunin is correct, you want to keep your tow bar as close to level between your RV and the towed vehicle as possible. So it really matters where the tow bar mounting plate is located on your toad, and the difference in height from the ground that your tow bar connection points are with the toad and RV. I believe most tow bars manufacturers recommend no more that a 4" difference in height from one end of the tow bar to the other end. The info that comes with the tow bar should confirm this, or you can find it on the manufacturers website.
Steve & Nancy
2005 Itasca Sunrise 33', W20 Chassis, Ultrapower, Henderson Trac Bar
2012 Chevy Captiva Sport AWD, ReadyBrute Elite Tow Bar, Blue Ox Base Plate, Protect-A-Tow