I've been driving and digitally ignition tuning a 8.6:1cr 318ci in my dailydriven Dart for well over 5 years and hardly got the mileage to improve noticably (10-11mpg).

I've now got a 11.3:1cr 360ci installed in the car which has significant more power more but the mileage is still the same.
The 360ci has a 208-210 cranking psi with its CompCams XE256H cam.
A518OD / 3.55 gears.

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. Noticing hard to rotate front tires lately, I removed front res.valves recently and promptly got the lost 1 mpg back.