Spatial Dependent Materials in HFSS?

I'm trying to create a material that has spatially dependent properties. In there a way to enter properties that are dependent on X, Y, or Z?

I have tried to do it in the edit material properties windows but it returns me an error that says I can't do spatially dependent equations. I have also tried to create a project variable, but there it does not allow me to enter the spatial variable X, Y, and Z.

Anybody have some insight on this?

Thanks.