The distance between two straight lines moving in two dimensions, how complicated can it be? Still, it's confusing to think about, and more difficult to explain.
Here are some reliable rules of thumb:
To raise the saddle 1mm, you need to plane the fingerboard down 2mm at the nut.
To lower the action 1mm at the 12th fret, you need to plane the fingerboard down 4mm at the nut.
What makes the geometry hard to visualize is the fact that the strings are pivoting from the fixed point of the saddle, while the surface of the fingerboard is pivoting from the sound hole.
Taller frets lower the action by 1/2 the increase in fret height--e.g. changing from .040" frets to .050" frets will lower the action .005" (.125mm).
Adding a veneer to the top of the fingerboard has the same effect as taller frets: a 1mm veneer will lower the action 1/2 mm.
On the other hand,
To lower the saddle 1mm, you need to plane the fingerboard down .67 mm at the sound hole.
To raise the action 1mm at the 12th fret, you need to plane the fingerboard down 1.33mm at the sound hole.
As you can see, it's much easier to raise the action than to lower it. For that reason, many builders aim for an action that's a little too low, and make adjustments by planing the fingerboard. You'll often see new guitars with fingerboards that are thinner at the sound hole.
To correct a guitar with very high action and a low saddle, I prefer to remove the fingerboard, pull the neck back to a better angle, glue on a new fingerboard to lock the angle in place, and plane the finger board flat in the new position. The neck joint is quite flexible with the fingerboard removed,
and this allows for a large adjustment without a significant change to the thickness of the fingerboard or the overall thickness of the neck.