Appreciate the thread for the idea of adjusting the garage door height in the absence of a lift gate adjustment. I now have about two inches of clearance thanks to having the garage door pull itself up and in a bit more.
Further, being on a step stool while adjusting the garage door revealed some undisclosed damage to the van's roof - a slightly larger than softball-sized dent with three slightly curved scratches in the paint that I am absolutely certain did not occur after I took delivery. There's no place I park where anything remotely like that could have happened.
Have called the dealer to see if anyone will admit to knowing about this before the sale and/or if they will just take responsibility and fix it, but having found it four days after signing all the papers (in the face of a somewhat contentious purchase process in the first place), I'm not sure what recourse I have if they try to say it wasn't there before. But at the very least I can touch up the scratches to ensure they don't become a corrosion problem later, so I guess that's something.