Hello Paul,
With the honeycomb tray the Gweike is able to lower 17mm, that will be 0 mm of material thickness. So the up position of Gweike is 0, which is the focus of 17mm material thickness.
If you want to engrave something thicker than 17mm you will need to at least remove the honeycomb (and maybe also the metal plate) and measure the distance to the laser. Measuring distance is instructed by this video from Gweike: Gweike Cloud PRO rotary tutorial with gweikecloud Online Software - YouTube (from 1:35 they are talking about the hight measurement).
But you can also do some math yourself and measure the distance from the top of the honeycomb tray (which is 17 in Gweike language).
Hope you can figure it out with this information. Otherwise I would suggest trial and error.