Well you are correct in some ways although I still go this deep on the smalled tracks and I don't have problems. The big problem is the board consists of 75micron copper, 70 micron ceramic and 160 micron aluminium. So Ideally I would land somwhere in the 70 microns of ceramic all the time but my CNC router (RoutoutCNC) just won't do it. It will start like that but by the time it gets to the other side its either to deep or not even touching the board.