From your description, it sounds to me (although I could be wrong) as if Vue automatically changed the shadows into "shadow map". Vue does this whenever you have a volumetric sunlight and you add softness  to it. Vue assumes that you want this because volumetric soft lights are fairly slow to render.

To change this, you edit the sun's properties, go to tab Shadows and uncheck "use shadow map". Of course, render times will increase. Alternatively, you can keep the shadow map and increase the Size in Quality section. I normally use 4096 for the size (this impacts RAM but I have plenty).

My soft shadows are also normally between 1 and 5%, like said above, or less (for example, my "bay of ortus" has 0.25% - look at the shadows from the leaves in the foreground).

Frank uses shadow density at 85%. This is the recommendation you'll find in many places, in order not to have pitch black shadows, which are not realistic. In former times, I also used to do the same, but not anymore. I found that, in certain atmospheres, setting the shadow density below 100% can create noise in the shadows and make a somewhat strange look. Now, I keep my shadow density at 100% and use "sky dome lighting gain" instead to compensate for that and have "normal" shadows, not competely dark. Almost all my images have "sky dome lighting gain". The intensity varies, but it can go from 0.5 to 10. I adjust it to what I feel is right in each situation, I don't have any "recipe".

If all of the above didn't solve your problem, you'd better post some screenshots of your results and your settings. Because your atmospheres are quite unique, your problems are also probably quite unique. :-)