The gas guages aren't linear. You probably showed full until about 40 miles were driven. Then, BOOB, drops to 1/4 tank. Just because it shows 50 at 1/4 tank, you'll still probably get somewhat more than 200m tank.
One thing I want to try this summer is increase the (adj) FPR. If I read the service manual correctly, mine (and many others) aren't as high as designed.
Sometimes people think less pressure gets better mpg. I think more pressure MIGHT atomize fuel better. It's worth a try...especially since a select few have reported better results...making me thing 16 city 20hwy isn't impossible.
(I'm at 14.5/17 now)
2001 Ebony VX and 1989 Custom 383 Corvette