TexFalloff question

[palosanto]

I'm trying to use the TexFalloff texture type in a new material to create a dust effect by placing a coat of white color on the upper areas of objects.
I want to be able to control the height where the 'dust' starts and ends.
I'm using the Towards/away method with Local z as the direction and origin.
The 'angular blend' values should be irrelevant for the Towards/Away method.
However, no matter what values I give to 'far' and 'near' parameters, I get always the same result.
I've tried other combinations and I can't make it work and I couldn't find any reference to it in the documentation ...
I'd appreciate some help.
Thank you

---

---