Help: PML Scaling Factor and Implemantation In RF Module

Dear All,

Can somebody tell me what is PML scaling factor and curvature parameter in PML of RF 4.4?
I am going to sweep a large frequency range 4.8e14-8.8e14 in my simulation.
The structure is easy. Air and Substrate. both are semi-infinite.
I wanna use PML surrounding the structure and finally calculate reflection.
I attached the file.
I appreciate if you reply.
I discussed this problem with more detail also in
www.comsol.com/community/forums/general/thread/46787/
Please help.

Thanks,
Mohammad