Hi Marvos,
To maximise the resolution you MUST do it mechanically.
Using either end point or DR at your eg of 40% is just that ; 40% of available (normal) travel.
As you can, with most servos anyway, use up to say 135% 40% is now just equivalent to 30% of actual available travel.
Therefore you only get 30% of available resolution.

So let's say, for the purpose of this conversation, that 15mm is the most you want on a particular surface.
Set end point to 135% (limit at 135% also) and DR at 100%.
Then adjust the links in on the servo horn or ,perhaps preferably, out on the control horn to give the desired 15mm.

Brian