Animation- Set unit flying height not working properly...

The unit has movetype "Flying", the locust ability, and no collision size.
I'm trying to set its flying height to -500. It doesn't seem to work. I tried using 500, in case it just wouldn't accept negative numbers, but that didn't work either. Any idea what could be the problem?

from what I recall, it needs to have a movement of at least 1, might that be it?

Probably needs movement. Negative does not work, by the way. At all. Unless, I think, you had the terrain moved up by triggers (not sure on that one).

You CAN set a unit to a negative height in the object editor, so...

EDIT:
You're right, it doesn't work with the trigger action...

So don't contradict people who know what they are talking about unless you know what you are talking about?