In my experience, the minimum height is at least 15 cm. Otherwise the suction head is too high to get under furniture.

I keep reading that the motor/dust container is too bulky and gets in the way. That's what I thought at the beginning of using my Triflex. But you can (in the configuration that this unit is attached to the bottom of the suction pipe) turn the "suction head" almost 45 degrees to the side and then simply vacuum under the furniture (under the bed in my case). But I have never measured the height.