When installing fenders you almost always have to make some kind of adaptation.

How much space do you have btween the rear tire and the seat stay bridge? If you have a fair amount of room, 3/4" or so, I'd use the "L" bracket idea to keep the fender closer to the tire. If it's close, I'd drill a hole in the fender itself and bolt it directly to the seat stay bridge. If you do the latter, be careful that the bolt doesn't rub your tire.