SphereMask ignores passed hardness value?

I use a dynamic instance of a material with sphere mask node. But strangely passing a hardness value as parameter or constant has no effect and hardness is always 100 when passing a value. Only setting hardness directly in the node works.

So this works as expected resulting in hardness 1:

While a parameter or even a constant like below gets ignored and always result in hardness 100:

Is there a way to pass a hardness to the sphere mask node during runtime?