Rear Window Defroster for the Lower Narrow Window

I apologize if this has been covered previously for the Prius Prime. This issue may be just the same "design feature" that is found in the non-PHEV Prius models, but here's my "problem."

The defroster heating wires on the upper (predominant) clear rear windows work just fine for me, but the narrower, darker panel does not appear to defrost well, if at all. I see that there appears to be wires inside that panel also, but I am wondering if they are not heating elements, or for some reason heat to these wires are turned off?

It's been rough couple of weeks here in Central Indiana, and I would like to know if this "feature" can be improved somehow.

Thanks.