I wouldn't worry about it. You could find discussions about de-rating the towing capacity of a trailer hitch due to extending it, but 3 inches is below the noise level. If you are talking 12 to 24 inches, you might want to de-rate it and compare the de-rated capacity to your Jeep weight. The height of the ball would not effect the capacity much either...even less than the length of the hitch.
2004 Tiffin Allegro 27.5 ft. P32 18,000 lb GVW. 8.1 liter. Workhorse chassis built May 2002. 21,000 miles. 2012 Jeep Liberty Toad. RVi2 brake unit.