This link is to a good thread on setting up a weight distribution hitch system. Keep in mind that the amount of stuff in the back of your truck- especially a lighter truck like the Frontier, will effect rear end height and, thus, ball height. Loaded up for a trip in my 2010 Titan, I can drop an inch before even hooking up a trailer. In other words, my ball height set-up with an empty truck can be different than loaded. THAT said- my hitch instructions say I should set it 1 1/2 to 2 inches higher than the the level trailer before hooking it up to account for settling. You are likely in the ball park- but if it comes down to being too high or too low with front of the trailer error on the side of lower in the front if you must "error".

RV.Net Open Roads Forum: Towing: Travel Trailer Hitch Set-up Procedure

Rick