WRX Wagon guys and Regular WRX guys Help

I have a sedan…but I’m not sure what help I can be based on your post. I can get like 28mph on the highway if I cruise at like 70-75. The car is chipped with full exhaust (no cats) amongst other things though. Around town, enjoying the car but not beating on it with a mix of highway I can average 18-20 mpg per tank.