16-17 in town. 20-24 on the interstates.
Your mpg sounds a bit low. Not many miles, so that's weird. Do you get on the gas pedal a lot? Even so, that's too low.
Maybe a tune-up, clean your MAF and PCV, or check to make sure your using the proper octane for gas. No use using 91, if 87 will do. Not sure about octane for the Cobra, though.
A free tip is to check your tire pressure every 1-2 weeks as that will make a minor improvement along with making sure your alignment is good. Of course, this is good for optimal tire wear.