You can host this face based family on a level or a plane. but the only way to control the elevation is by the built-in “Default Elevation” type property:
For a more fine-grained approach, you’ll have to rework the family and set up an offset parameter and then modify your script with the new parameter in mind. Alternatively, you could use a different family template for your lights - face based families can sometimes be more of a hassle than they’re worth.