Yes, sorry- XL. The back end is sized to fit over top and side cases. If you ride without them, you'll have some slack in the back.
I also tried the Oxford Umbratex. I can confirm that size "L" is annoyingly tight. If I bought that one again, I'd go XL.
Last thought: having these half covers is a game-changer for me. I first started using them years ago when I lived in PA, where I used to do more moto-camping. It's so nice to wake up after a rainy night with a dry seat and tank. The cover frees up a lot of tent space, too: I started leaving my helmet on the bars, jacket on the seat, and luggage and tankbag on the bike - all under the cover - everything dry and concealed even in all-night downpours.
I've even used the cover as a makeshift poncho to keep me dry. In an emergency, it could sacrificed for use as a bucket, as cordage, as bandage, as signal flag, as shelter, as clothing. It really earns its place on the bike, IMO.
Probably keeps presumptuous passers-by from swinging a leg over, too.