May be I've got the same package with kick-panel insulation? I have mine from Year One.

This third piece goes directly under the driver side kick panel, between metal body frame and plastic moulding, covering the door hinge area. The one small screw, that holds the kick-panel, goes through it...

I know that cause I kept the old one (when I had this new part in my fingers I've had the same idea to ask here in the forum where it goes to ). There is no "shape" that will fit this part and make it obvious where it exactly goes... it's some kind of "free flowing". On your pic it's upside down, the one corner off is because the park brake pedal.

But the worse thing is, there is SUCH A PIECE ON THE PASSENGER SIDE TOO, a fourth piece, which is not in the kit!

IF my car had those insulation right before I took it off.