The legs are designed to be most stable when you take them out fully. If you make the legs as stable as possible and the metal rod as high as possible, it's 15 centimeters. Not 20 centimeters. If I try to make it 20 cm, the legs will slide.
If I could re-choose, I would buy a stand which could be 21 cm with flexibility. I've propped it up on a box.
It's also pretty wide, so on a small table you might have trouble fitting a laptop behind it. Anyway, it's not bad, it's just small and wide.