Hello. Just joined the forum - was googling a problem I've encountered in my new 2019 Odyssey EX.
Was relieved to see others have the same problem I'm concerned about - inadequate tailgate height when fully open. But very disappointed at the same time since it seems it is a design flaw with no quick fix by taking it to the dealer. When we bought it, the dealer actually glibly told us the tailgate height was adjustable and we took him at his word. Turns out there is no adjustment in the EX.
P.S. Would be interested in a signature campaign to send this concern to Honda. Won't hold my breath though.