Hey, the gas quality has a lot to do with it. I had a 2014 Honda Accord Hybrid and I ran hi yes and the gas mileage was great all the time. On my 2018, it must be tuned for only 87 octane and does not do well with hi test. I do run the fuel dry every 3rd take full and maintain 45 mpg. Otherwise, my fuel mileage varies more. The tuning and the gas quality is my focus. I read it is not recommended to run fuel additives. I keep clean engine air intake filter. What else can be done?