Hfss thin film resistor

Hi to all
i have a great problem with hfss. I'm trying to simulate a thin film resistor with a strate of alumina and above a strate of tantalium. i have attached a file with the imageg of my structure. i have an air box around the resistor with radiation as boundary condition, and i have used Perfect E boundary condition as indicated to have a common ground plane. in the forum i have read that in this case it could be used RLC as boundary condition, but i don't know how it can be used. Could anyone help me to correct my model?
thank to all

If someone could help me in this post i have attached the file with my project...
Thank you