To see the Ford's advertised range, charge your Lightning to 100% then reset your driving history on the vehicle’s touch screen: Settings/Charge/EV driving history (press and hold to reset). Before resetting, if you want to see your driving history, go to the FordPass App and select Vehicle/My EV driving.
I had the same full range concern since my extended range Lariat showed only 270 miles (instead of 320) at 100% charge. I spoke with Ford and the agent explained that my driving history is part of the range calculation. Since I recently had a 200 mile highway trip at ~72 MPH, my range at 100% charge was (predicted to be) 270 miles instead of the expected 320. To prove this, I went into the Ford's touch screen (not Ford Pass app) and reset EV driving history. My Lariat was 100% charged and the range suddenly changed to 320 miles. Tesla does not include your driving history in the range. At 100% charge, my Tesla MX always shows the full range of 328 miles. (Perhaps there is a setting to alter that, I have not looked.) Obviously, I get ~25% less than that in the real world.
I hope this helps.