Thanks. I see the transition now.
In the pictures above, a static mesh plane is intersected by a sphere, cube and cone (all with a transparent material). The DistanceToNearestSurface-Material covers the static mesh plane. So, for the lerp alpha should be ~0 at the intersection areas such that they are painted white. But it’s just the other way around. Why is that? How can I modify my material, such that the intersection areas are precisely colored?