I'm of the same opinion. I've been driving and tuning a 318ci in my dailydriven Dart for well over 5 years and hardly got the mileage to improve noticably.
I've now got my 11.3:1cr 360ci installed in the car which has a significant amount of power more but the mileage is still the same.
The 360ci has a 208-210 cranking psi.
Last year I had installed residual pressure valves in the brake system. 10psi for the rear drums and 2psi for the front discs.
The front disc pressure valve was good for 1 mpg loss in mileage. I removed it recently and promptly got the lost 1 mpg back.
