As you can see at Airstream FAQs
it looks like they're saying 18.75". I've seen things like that is to the top of the ball before you hitch up... which is nearly meaningless due to variable squishy-ness of suspensions. Are the tires the same size as original (more than likely). Best thing to do is try something close to the recommended height (or anything really), engage your WD bars and stand well back and look at it. Better yet, take a picture and post it here.
Measure to the top of the TV's wheel enclosure sheet metal before you hitch up. With WD properly engaged the body of your TV should settle equally front and back. Cinch up your WD a bit (links on a chain?) until it gets close to settling equally -- nothing is perfect y'know. If the trailer then looks high at the nose I'd consider lowering the ball a bit since you do have a pretty stiff suspension. Then
post a picture and ask the experts here what they really think ...
And Alden -- a belated HAPPY BIRTHDAY!! Hope you have a fun trip.