I must have too heavy of foot
I get 13.8 in all city and 19.9 at 70/75 in all highway driving.
Of course the 3.64 gears have something to do with the highway miles.
I was getting 14.1 in town and 23 highway before I added the extra fun
My E32 740 had a highway range on the OBC at 70 mph of just over 500 miles. Long time between Pee stops