Ok, I see. I can't say that I understand what it is that is filling the voxels up.
This is the settings I've been running with:

Texture Type: Perlin Noise
Coordinate Method: Fixed

Dropoff Shape: -Y Gradient
Edge Dropoff: 0.400

Any idea what I might benefit from changing? I would glady play around with It more but the render is painfully slow on my computer so anymore hints would be grately appreciated.

Also I've tried to turn the Shading Quality > Quality up from 1.000 to 3.000 but that didn't seem to do any difference.

I attached a picture with my settings of opacity and shading quality.