Originally Posted by Eric F

In my understanding, this is accurate. Rolling resistance is only one factor in the story of how efficiently a tire gets down the road. Aerodynamics play a part (in conjunction with the rim). Hysteresis loss plays a part. Vibration and vertical deflection losses play a part. The best tire and pressure choice finds the balance that minimizes all of them as much as possible. When you get outside that balance point, minimizing one factor increases another, and the overall result is diminished.