Congrats on your new trailer! The two happiest days of any trailer (boat, car, home, airplane etc.) owner's life is the day you buy it and the day you sell it!!!
Anyway, it is my understanding that the 18 3/4 inch hitch ball height on your tow vehicle is at the top of the ball standing level & unladen. The proper height is important because it has an effect on the trailer axle load. If it's too low, there is too much weight on the front axle, too high and your're overloading the rear trailer axle. That also affects handling and braking, and changes the geometry on the stress points on the chassis of the trailer. Remember that a two inch difference at the hitch end can make a larger corresponding difference at the bumper end cantilevered over 32' as it rises and falls over bumps down the road.
Other folks here can give you the exact hows and whys, but in a nutshell, I believe that's the issue.
Forum members... is this right?
AIR 2053 Current: 2006 Born Free 32 RQ Kodiak Chassis, & 1995 Coachmen B-van
Former Airstreams: 1953 Flying Cloud, 1957 Overlander, 1961 Bambi, 1970 Safari Special, 1978 Argosy Minuet, 1985 325 Moho, 1994 Limited 34' Two-door, 1994 B190 "B-Van"