After my Moto Guzzi 750 and my KLR 650, my Concours seems to be a gas guzzler as well. I regularly got 55-60 mpg with those smaller engines, and it seems like I'm filling up a lot more often. Riding 2 up, (which I know is going to use more fuel) I got exactly 180 miles before hitting reserve, 160 of which were at 65-70 mph, and the last 20 at between 85-90.
I always got 200-250 miles per tank riding 2 up on the guzzi, (5 gallon tank) but I almost never went over 80 with 2 riders on that one.
Never rode 2 up on the klr, but with its 6 gallon tank, I always got 250 miles per tank no matter how fast or slow, on road or off. I miss that...