Sorry, I forgot that some of the RS cars had small wheels, my Redline has 18s.
The DISC is driver information center. If it hasn't been reset from before you started driving it could be displaying lower than actual MPG. It's very common for cars to come off the dealer lot with single digit lifetime fuel economy.
The big culprit is the short trips with multiple stops.(the higher speeds don't help either)
My hatchback has the bigger spoiler, the bigger wider wheels and tires, and on a commute of 21 miles, I have a section that's 14 miles long uninterrupted and I run at 50mph. Car LOVES that, I routinely see 50mpg+ averages on that road. Add back in the mpg from my slower neighborhood area with 5 stops signs(about a mile of 30mph) and a few miles at 65mph and another stop sign or three and my mileage for any given day drips down to 38-40mpg.
Lifetime average on my car at 15000 miles is I believe 33mpg. 28mpg probably during the winter I where I run
a defrost I all the time, and 38mpg during spring where I run windows down mostly.
I NEVER go on trips less than 10 miles, I don't sit in any notable traffic, and I don't exceed 65mph. Probably 65% of my miles are 50mph back roads car loves that.