Your accord is likely 18 inches lower, a whole lot more aerodynamic and approaching 1000 lbs lighter.Bump the tire pressure up to 50 and I bet you get to 17.8
Btw my 06 3.0 Accord gets 21-23mpg. The only time it does well is on a straight highway trip. If I burn a full tank in one day non stop highway I see 31-33