Interesting observation, flying indoors with no GPS (or possibly very weak GPS but no GPS indications) and all visual sensors turned off, Go4 shows ATTI mode. But in fact the upper IR sensor does still operate at about 4 feet from the ceiling, the M2P altitude is limited, trying to increase altitude doesn't work. A red upper obstacle warning is shown. So just to be absolutely sure that the sensor was the only limiting input, I taped a small piece of paper over the sensor and there was no altitude limiting anymore. A nice feature but I wonder why its just not a switch in the sensor settings. Maybe DJI figure there's no reason for you to want to fly close to an upper obstacle.