GHH Plat Max - Question around estimated mileage on full tank

Sorry if this has been answered. I've seen the posts around the gas tank being 17 gallons, but hitting empty at 12. I've experienced that. Not a huge deal.

In addition to this, I've noticed that the estimated mileage on a full tank when I fill up around 12 gallons, is around 340/350 miles. But, by the time I need to refill (0 estimated miles remaining, just says refuel), I've driven around 275-285 miles total for 12 or so gallons. Anyone else notice this?