The study of the Antenna is a science in itself. There aren’t many people that truly understand or can predict how an antenna is going to work, me included. But some thoughts crossed my mind when reading these replies. Every book that I have read on antennas cautions you against installing it near a metal structure. I don’t know if caution is the proper word, it implies that there is some danger involved here but there isn’t, perhaps suggests is a better choice. It seems to me that running an antenna around the window opening or under the dash or under the frame, floorboards or for that matter, anywhere near the metal framework would give you pretty poor reception.
The reason most antennas stand up vertically is to grab the signal out away from the metal and because of the polarity of the transmitted signal.
In my opinion, if you want the maximum performance from your antenna, I would install it where you see 99% of them installed, that being on the cowl.
Denny Graham
Sandwich, IL