Maybe I'm misunderstanding, but that doesn't quite make sense to me. You're saying the 4 ah cell is smaller and heavier, but the cells are still 18650 format so the size doesn't change. I suspect there is a gravametric improvement. In the London video, Elon speaks to batteries becoming more energy dense gravametrically, saying that he sees a clear path, over the next 5 years to around 280 Wh/kg. It's common to here of gravametric improvements, but quite rare for anyone to mention watt-hours per liter.