John,
I have mine set in the rear most position, height in the middle setting. This gives the most clearance to the cab on our short bed trucks. Where you set your height position depends on how your trailers pin box is set up. The middle is probably a good starting point to see how much clearance you have between the truck bed rails and your 5th wheel. You should strive for 6" or more of clearance between the bed rails and trailer, and along with that having the 5th wheel riding as level as possible. Try this and see if you need to make adjustments. The B&W will adjust up/down in 1" increments. I don't know what pin box you have but mine adjusts up/down in 2" increments.
Rich