I believe that at "E" you should have 1.6 to 2.0 gallons of gas as a safety measure. According to spec 19.1 is the size of the tank so at "E" you would only be able to fill 17.1 gallons and if you are not at or bellow then you can see why 16.5 would be the case. I have a 2012 and have never gone past 17.1 or so most of the time 16.? would be the norm. I wouldnt be too concerned with it.
This may sound silly to some, but I rarely put more than 10 gallons in the car for several reasons. The most important is that if your tank is always about half full instead of full, you aren't carrying around that excess weight and might improve MPG by as much as 1 MPG.
Second reason is that if you do not drive your car on a daily basis (mine is driven less than 300 miles per month), you have less chance of having your gas go stale. We had a situation here where the gasoline supplied by Exxon actually had some impurities in it that damaged some cars' engines. The refinery rushed new gasoline to the affected stations, and issued directions to people who had bought gasoline from a whole list of retailers that they had provided. They instructed that drivers should dilute the contaminated gas by capping off their tanks every day, thus blending the good gas into the bad as quickly as possible.
Third reason is that seasonal rates of gas prices fluctuate almost daily here. If you don't keep a full tank, you can take advantage of these fluctuations when they move in your favor.
The most gas I have ever been able to get into my 2010 R/T was a bit shy of 16 gallons when I took it on a trip to Alabama.
