I've created a very simple model in CST Studio Suite  which involves a plane wave incident on a custom defined Normal material (I want to investigate the effects of materials with different reflection constant). However it seems that no matter what I change the conductivity to, I don't seem to get any reflection from the surface, as measured by a field probe above the surface. I have had the conductivity as high as 10^8, at which point I would expect a full reflection, however I'm seeing next to no reflection. Why is this?