Engine compression.

Hello, this is my second post as a follow up to my car problems. Just bought my rx8 maybe 2-3 weeks ago. Mazda dealer said its 99% likely I have an engine compression issue and need a new engine but I can't get it diagnosed or anything done until my extended warranty goes through. So I'm hoping this warranty company will cover it or I'm screwed. Felt like I regret buying this car entirely but hey what's done is done. Anyways my question is can engine compression issues lower gas mileage? Cause I just got a 107.3 miles on roughly 12.68 gallon tank. That's like 8.4 mpg.. And that's all city btw.