[Threshold]

That's because the 'pivot point' of the object is in the centre of it, not on the side that you want it to pivot from. So if you rotate it, it's rotating from the centre of the object, not the end of it.

To accommodate for this, you just need to adjust the X, Y and Z values until it looks like the desired open position that you want..

Some helpful callbacks/functions:
https://sampwiki.blast.hk/wiki/MoveObject
https://sampwiki.blast.hk/wiki/OnObjectMoved