for double and single sided work using a 60 degree bit i set the depth by runing trial scores and viewing them through a graduated microscope. I set the width of the line to the tool manufacturers min and max limits or anywhere in between to suit the artwork requirement.
So i do not worry about depth since the isolation is main concern.
On inner layer cores i use square endmil and this is where the depth becomes critical as the core laminate is only 0.2 mm thick.
As the square endmill tool is constan width i select a tool diameter that will meet isolation requirement and only cut into the laminate at a minimum depth consistant with removing copper. I use a floating head with a threaded pressure foot which allows precise depth setting. The foot is sdjusted via a threaded lock nut.. thread pitch 1.5 mm.and a i have 72 detent notches around the lock nut periphery which gives me 0.0008" increments, a good feel for depth adjustment.
See how the numbers come out?