arcmap - Way to set a label leader line length (not using annotation) in ArcGIS Desktop?

How to set a label leader line length without using annotation in ArcMap 10.5?

• I am using label leaders mainly for labelling features - pointing at the polygon/line/point that the label refers to.

I use Labelling Toolbar - Label Manager, than go to Symbol (/Edit Symbol/3rd tab - Advanced Text/Text Background - Properties) .... Line Callout/Leader Symbol (/Edit Symbol/Cartographic Line Symbol) ..., using simple line or arrow line mainly

example:

In this example I have set an offset that determine how far the label from the polygon border would be, but I cannot set internal zones (going from the dialog on picture bellow to properties and on the 1st tab internal zones) to influence where the leader will have it's end... which would I think answer that question - so I am looking for another way to do it.

illustration