Gearing looks like:
which illustrates the compromise of derailleur gearing on small wheel bikes: you have to use tiny cogs or huge chainwheels to get higher gears. Compare this to a Hummingbird or BikeFriday pakit 54x18
fitted with a Sturmey-Archer X-RF4* giving gear inches of 40, 52, 66 and 85.
*which seems like a lot less trouble than designing a proprietary hub, cogset and derailleur.