Nah, more so sharing my experience with a new and unfamiliar truck and I'm new to the FCA family anyhow maybe its just how it is. So of the past vehicles I've owned (for discussions sake) if the stated capacity was 20 gallons and I ran it uncomfortably low with DTE saying 10 miles, I could expect to fill the tank with 18 gallons. Not that I run my tanks that low typically, that seems foolish to me, but you know it happens sometimes especially *when your lousy brother in law borrows it for the weekend while your away and leaves it on fumes. So in those situations it seems that a 10% cushion is built in or there is some margin of error in the gauging system. Whether the vehicle actually had a 16, 21, or a 36 gallon tank as in my last F series- the approx 10% seemed to me to be a recurring trend for gauge accuracy ("So my 2017 is not reading accurate either") based solely upon my experiences.
So while you say mine is 'not that far off'-and I cant disagree that its probably not that far off, it;s farther off than what I'm used to, hence the post, and since I read up on this before buying the truck its enough of an issue that I'm not alone. I agree about the variables and the biggest of those may be about what your 'used to' I guess, and I will get used to this truck. Lastly since you bring up an interesting point I wonder how much 'dead space' is built in to the tank for volumetric expansion aside from the fill tube and vent.
*The exception to my experience being a BMW sedan that was dead on the mark when at 2 miles DTE it stalled on bridge only 2,000 feet away from the pump....thanks again lousy brother in law. My 2 fuel station stops are showing closer to 20% for the Ram.