vray distance tex holy grail

seems I´m not member of the few selected ones understanding the VrayDistanceTex options … I read the help, crawled the forum, still ignorance and no enlightenment.

I´d like to use something some simple geomety like a box sitting in the terrain surface as a mask (grass outside, gravel inside…). I managed to do this with a hard edge but I´d also love to have a soft blend between the inside and outside. Anybode now´s the trick?

Thanks in advance, Matthias

You just control it with distance (cm)

Key is to untick all the stuff.