ok, let me try and understand this. You can't adjust the coil up or down as a whole? or you can only adjust the spring up and down?
I'm thinking you are moving the spring up and down? so basically adjust spring load, not height.
I'm thing you're only moving the 2 collars that the black arrow is pointing at. You should be loosening the 1 collar the white arrow is pointing at. The white one is the one to move the assembly up and down to lower or lift the car.