Because light is losing lux with square root.
I can not explain it well or with right words but to double throw, you need to get 4x candlea/lux.
100lux = 20m
200lux = 28,3m
400lux = 40m
This is with the ANSI standard, i think it is 0,25lux at throw distance.
So GTvn is 1,75mil lux = 2645...