new overlay Material -> no Parameters to change ?

Hi,
I was not able to find a solution how to change a Parameter of a Material Instance, when I use it as the new Material Overlay (5.1)
is there any new way ? or is it not yet possible.

the Scalar Parameter references to the Mesh Material, but not to the Material Overlay.

thanks,
any help appreciated

Did you found it?

What did for now is creating 5 variations of material and swap them based on some logic, but there is no transition.