Keep in mind that the average speed during the EPA highway test is
48.3mph.
Then consider the fact that:
A: Most vehicles are traveling significantly faster than that (sometimes over 70)
B: Many of them have higher Cd than your coupe, and
C: Aero drag is a substantial factor at high speeds,
While some vehicles may be geared to be efficient at higher speeds, the consensus around EM is that high speeds usually result in increased consumption; I imagine that to be true of trucks and SUVs.
The high speed test would likely be a better real-world indicator.
But hey; it's about how you drive the vehicle you already own.