I have had 2 dealers tell me that you want to have at least 6 - 7 inches between the bedrail of the truck to the bottom line of the gooseneck. We have had 3 trucks in the past 5 years and have set the fifth wheel hitch (reese 16k) to match this clearance on all 3 trucks and surprising enough the 5're have all been level and pull straight. Our current truck is a 09 Dodge 3500 4X4 single rear wheel that we have set the hitch as above. We only have used the reese 16k so having a different kind of hitch (slider or B&W), I'm not sure how to raise or lower that type of hitch. Nat