I am a little confused as to what you are trying to do.
WIDO_SILL_HEIGHT is a value calculated from the height of the door or window from the base of the wall it is placed in.
It is not a value you can set in the object script as it is not a parameter like height and width (A & B).
While you are scripting it may always return a value of zero as you object as yet does not belong to a wall.
It is not until you place an instance of the door in a wall that it can determine a value.
You can force it (for testing) in your script by saying WIDO_SILL_HEIGHT = 0.100 in the master script but you will need to remove that line when saving the object for real as otherwise it will always use that value regardless of what height you place it.
Versions 6.5 to 22
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision M6800 - i7 4700MQ @ 2.40GHz, 16GB RAM, AMD FirePro M6100 (2GB), Windows 7 64bit