Gas Tank Capacity 2006 Prius?

I found that turning the gas nozzle upside down before inserting it into the filler opening gets me much more volume and almost never triggers the pump to shut off too early. Still, in the winter my capacity is lower than in the summer. It's not that bad for my case, though. I can do 9ish gallons in the winter, sometimes 8ish, but never anything like 6ish.