Microwave doppler sensor sensitivity? Window is a problem?!

I've hooked up the doppler microwave detector to a raspberry pi 3 b+ and have been bench testing it -- and it works fine waving my hand in front of it.

I've moved it to the area where it needs to be detecting and it doesn't seem to work through the window! It's a double pane window, and I'm standing in front of it moving. My foot is moving inches from the window and the detector leaning against the window. The sensitivity is set all the way up to just below where it triggers constantly with no motion nearby.

I don't understand --- my understanding is this sensor should work through walls and glass.

Or maybe not?

Even using the lower frequency 10 GHz spectrum means that 5G coverage would only exist inside of untreated glass windows, but likely nowhere else inside of a building.

What the heck is untreated glass?

Is it possible I have a defective unit? (Purchased locally through Jameco.)

...just to make sure also I have the orientation right -- the most sensitive side is NOT the side with the metal box, but the opposite side. Which orientation also has the widest spread? The card positioned in portrait or landscape?