Just reread the manual and it is 300 CM or 9.8 feet.
The StarpointTM Positioning System is activated by default when the aircraft is turned on.
•The StarpointTM Positioning System works both in GPS and ATTI modes and is only valid when the aircraft is between 30cm and 300cm above the surface.
IMPORTANT
The performance of the StarpointTM Positioning System is affected by the brightness and texture of the surface over which the aircraft is flying. The ultrasonic sensors may not function accurately above sound-absorbing materials. Please try to avoid the following situations:
•Flying over a monochrome surface (e.g. pure black, white, or red) or a highly reflective surface (e.g. water, transparent surfaces).
•Flying over extremely dark or bright surfaces, or in an area where the lighting changes frequently.
•Flying over surfaces with unclear patterns or texture, or highly repeating patterns or texture (e.g. tiles with the same design).
•Flying over surfaces (e.g. thick carpet) that can absorb or deflect sound waves.
•Flying at a high speed: over 8m/s at a 2-meter height, or over 4m/s at a 1-meter height.
•Flying over moving surfaces or objects.