I looked at the rhode's specifications and it's 7 cm max.

Hello,
The top of my desk is 4 cm thick, so it wasn't easy to fit because of the rotation of the arm.
Finally, I also wedged it against the wall to stabilise the force of the lever.
I'm not sure about the 8 cm.
But normally there's also a small support that can be placed on the desk.
Have a nice day.