I would love to understand their reasoning for not making the tank as large as absolutely possible though.
Maybe not worth the extra cost of all the work required to absolutely fill the trunk with fuel? 22 minutes spent refueling is incredibly low either way.
There is a weight trade off. Liquids like fuel are dense. If they filled the entire trunk with fuel it would have added another 500+ lbs to the car, possibly requiring additional suspension changes.
Maybe not worth the extra cost of all the work required to absolutely fill the trunk with fuel? 22 minutes spent refueling is incredibly low either way.