The jump between 500m and 2000m altitude is just too big for many multiplayer servers with lower visibility settings. 500m UAV usually gets shutdown, 2000m you wont probably be able to see ground, or objects on the ground. (in cases that server settings overrides your own settings)

Updating UAV terminals, so that you can enter your own altitude, would be noice, or at-least add an option somewhere in between.