Fill effect as mask + Material mode only support basecolor output
The Fill effect (as Add effect) in mask slot doesn't support different outputs (but only a basecolor) if you use material in grayscale input. Say I want the default Conrete Clean material to be masked out by its height channel via placing it additionaly in mask\fill effect\grayscale slot. It is important to have it that way, because of UV scale\offset\rotation parameters which are avalable in fill effect. If you try to use material in Mask builder you will only have scale adjustment which is not enough.