I have run these experiments in my lab over the years and I can tell you with 100% certainty that plastics can cause some loss to a radar head mounted behind it.
Depending on the shape, thickness, and angle you can lose minimal to significant sensitivity if mounted in close proximation to the material.
These losses may not be across all bands but may be specific to a band or for Ka may be specific to a range of frequencies within the Ka band while other areas of Ka may or may not be affected.
It is best to move the unit into a clear opening
Second best is to make sure you leave at least 1 inch of a gap behind any low loss materials.
If you mount behind metallic paint you are not doing yourself any favors regardless of leaving a gap.
If you mount behind chromated plastic, you can forget about any advanced warning as the chrome will prevent the radar signal from passing.
Good thing I just read this.
I've been hooking mine up all day.
I'm looking now for what to hook the mute wires to?
I found the mute wire for my radio, but the 9500i kit has 2 wires to connect??
I don't know where the second wire is supposed to go.