400ft above ground level may be the recommended max height in USA and some other parts of the world, but it is by no means a universal rule (if it is a rule) for the entire world.
Regulations aside, the max above take off height is likely limited by battery power, especially with the slow 2m/s descend. Assuming you can go up at 5m/s and down at 2m/s, the highest you can go and not crash would likely be around 1250m up (4 min up, 10 min down). That's pretty aggressive since full throttle up for 4 min up will likely burn battery at 2x hover rate, so that flight pattern take as much battery as a normal 18 min flight. I suppose one can go higher to maybe 2500m if they let it drop on manual mode to descend nearly without battery and spend like 8 min straight up at full throttle.