The efficiency goes down with smaller blade sizes (more losses to vortexes) so from the photo 20 min is the max to expect with regular lipo batteries.
https://youtu.be/u2v1QLmhNxM
It actually appears both spellings are currently accepted in dictionaries, but in the fluid dynamics literature you will essentially only find "vortices", so that's a much better (more searchable) word to use.
The efficiency goes down with smaller blade sizes (more losses to vortexes) so from the photo 20 min is the max to expect with regular lipo batteries.