"To avoid unnecessary danger caused by insufficient power, the aircraft automatically
calculates if the battery power is sufficient to return to the Home Point according to the
current position, environment, and flight speed. A warning prompt will appear in DJI Fly
when the battery level is low and only enough to complete an RTH flight. The aircraft will
automatically fly to the Home Point if no action is taken after a countdown.................................."
I.e. the drone determines the threshold for low battery RTH and it depends on at least the distance and height of the drone.
I do not know if it can factor in wind and or any required climb to RTH height.