It's a backwards world.

So, maybe I am missing something here.....

http://www.ebay.com/itm/79-HONDA-GL...ash=item56731d4c4c:g:Jj8AAOSwqu9VIGol&vxp=mtr

Someone went to a lot of effort it mount it backwards.

I suspect it wasn't fitted in the intended orientation on whatever it was mounted to because the flat rear was more usefully mated to the rear of something else than the curve was.
I'm thinking solo seated bike with another luggage trunk immediately behind the seat, and that one there behind it.