So those figures are basically gain ratios AFAICT.
FWIW the 16″ with 45mm cranks in most of those videos would be 4.52 on a chart like that and my pink 20″ with 45mm cranks would be 5.64, for those that want to compare with a setup listed above that they are familiar with.
I worked these out as follows:
- (16×12.7)/45 = 4.515…
- (20×12.7)/45 = 5.644…
Of course just having the same rough gearing is not everything. Tiny wheels and cranks with almost no movement add even more complexity.
But yeah a 16″ setup like this is not great for getting up hills! 
Side note: When I last went racing against @rogeratunicycledotcom on penny farthings in the summer he was at one point cycling a 50″ penny with 89mm cranks (IIRC… though he can correct me if I misremember), which would be 7.13!!! 
- (50×12.7)/89 = 7.13483146067
P.S. @rogeratunicycledotcom you need to start selling proper 45mm cranks as shimming these ones which were designed for something else is a pain. Clearly the unicycle world needs proper 45mm cranks… amirite @PedalSprell? 