You can measure this. It takes a nice depth gauge though as you will go for 100/s of a millimeter...

Take off the rotating back of your Linhof and carefully measure how deep the gg is set. I Measure every corner and take multiple readings to adjust for stupid. Then add a film holder with a donor-sheet of film inside, remove the darkslide and measure onto the emulsion. Compare and adjust your gg accordingly.

On LF repro cameras that would shoot from the top down you were recommended to use a vacuum film holder to keep the negative from sagging through gravity... shows how critical even a bit of distance is.