Open the editor on any terrain, I'll use VR for the steps.
(use multiplayer editor so it's easier to see the helicopter changing elevation when running commands, don't have to close the debug console)

Place a player unit in the editor.
Place a helicopter (I've tested it with Ghost Hawk and Huron) and set it's variable to heli, also make sure it's in the air so it spawns hovering.

Then go in-game and run the following command: heli flyInHeight [10, true].
With ASLToAGL eyePos driver heli in the watch view see the helicopter going to an elevation around 20 meters (when on VR).

Then giving it the command heli flyInHeight [9.9, true] see the helicopter moving to an elevation around 10 meters.
Giving it the heli flyInHeight [10, true] command again will see the helicopter moving to an height of 20 meters (when on VR).

Tested both in 2.13 and now 2.14. (also tested in 2.12 but with default syntax, no force).

While testing this I've also noticed that the default syntax heli flyInHeight 10 seems to ignore any values given after the 9.9 meters.
Even when giving it an height of 100 it won't move above the 10 meters. (until you use the force alternative syntax).