1. The WDH is to be set up with air bags at their lowest PSI and if a truck/SUV has auto level, it gets turned off.
The WDH measurements should be by the book, and the truck should look mostly level or slightly weighted at the rear.
2. NOW turn on auto level or inflate the bags to your desired PSI.
Manually adding air to the bags at this point is NOT to level the truck but add spring rate and improve the ride. If they level it out a hair...no big deal.
The WDH should absolutely be the primary leveling tool, but if as mentioned, the Hensley is already jacked to the max with 1400lbs bars then by all means...air bags can used to complete leveling. This should not be confused with standard adjustable heads of other WDH's, including the Propride.
I'd verify tongue weight to be sure one is not over the 1400lb tongue limit...there are too many Hensley failures out there that assumingly look like they were overloaded.