18650 batteries have maximum capacities of 3400 mAH and higher. In theory, the maximum capacity of a given size battery should be proportional to its volume. So a 26650 battery, which has a volume that's (26/18)**2 = 2.08 times the volume of an 18650 battery, should in theory have a maximum capacity of at least 3400*2.08 = 7100 mAH. But in practice, the highest capacity 26650 battery I've seen is Orbronics 5750 mAH battery. What gives?