I may have a solution for you. My CNC material height varies by as much as 80mm, I have both a variable height bed and powered Z axis, both can be in play when material height changes.
@LightBurn describes the optics very well in the link you reference. The online documentation is very good on this topic also. Given those references, I made sure to mount my camera directly above the center of my CNC work area. This gives me a center point alignment reference (of both camera image and table) that is independent of scale factor (the Width and Height controls in the Camera window). Thus when my material height changes, I use a substitute “alignment card” referenced at center of table to adjust the image scale, after sometimes nudging the X-shift Y-shift values to ensure the center points are aligned.
The technique is described in more detail here - Good manual zoom 10x 8MP camera for large CNC tables