Let's give a try, since nobody seems to want to respond. The distance between strings and the fretboard varies. The key to a proper set up is that the distance between string and top of the frets is variable to provide for the vibration of the strings. In general, the height of the string at the nut, must be just a little bit over the top of the first fret (maybe one third of a mm or so). The distance between a string and the top of the fret at the 12th fret must be between 3 mm and 4.5 mm for a comfortable playing (classical). It can be from 2.2 mm to 2.8 mm in some flamenco guitars, where some buzzing does not matter. Now, the thickness of the bound strings (E, A, D, and even G) is large compared to the nylons strings, so when they vibrate, they will demand a higher action to avoid buzzing, so some luthiers sand the fretboard at the bound strings a little bit more than at the nylon strings. Others do not do that, instead they provide a slanted saddle. If that is the case, one mm difference between the ends of the saddle should be fine. Does this address you queston?