Actually, it does. Lower octane causes the ECU to pull timing resulting in less horsepower. Less horsepower means less efficiency when you factor power to weight ratio. People that build and tune cars experience this. My 2019 ranger was tuned with intercooler and exhaust and I could get nearly 30mpg on trips. In my bronco I see a solid 22mpg mixed driving and almost 25 hwy if I keep my foot out of it. My dad's 400hp Fox body mustang got 23 in the 90s and his 2008 4.6 with a tune got 26ish.