physics builder linking user defined material property to variable

Hello,

I am building a transverse thermoelectric package in the physics builder. I want to use a user defined material property as variable. I add the material property to the Thermoelectric Model "feature" node in the .mphdev file. When I do this with built in material properties such as thermal conductivity, it works fine. However when I do this with a user defined parameter (Seebeck coefficient), I get an error:

Failed to evaluate variable.
- Variable: mod1.tee.S
- Defined as: material.S

Basically, I need COMSOL to use the parameter as specified for each material not a single user input. From the error I can see that the material parameter is not linking to a usable variable. I created a Material Property Group and defined the Seebeck coefficient there. I have also tried creating a Physical Quantity node under the Definitions Library to no avail.

It feels like the solution is right around the corner. Any help would be much appreciated!

Thanks,
Charles