It wouldn’t surprise me to see a Fit owner get worse mileage than a Civic owner. The 2012 Honda Civic with a 1.8L and auto is rated 28/39. The 2012 Honda Fit with an auto is rated 27/33 or 28/35, depending on trim.
With ratings like that, you’re likely to see driver-to-driver variances being bigger than the model-to-model variances…