Larry- Perhaps someone here who knows the theory could briefly cover impact of antenna impedance when the antenna is used for receiving.
I am posting because to me it seems the essence of your question is vehicle broadcast radio reception differences between various vehicle models.
That is a big subject probably best suited to an article.
Consider that a vehicle antenna may have a directional pattern, and you need to be driving in the same direction and road when comparing. VHF FM broadcast propagation changes and the effect is more pronounced at distance. You need to make a comparison between vehicles under similar propagation conditions.
I think if you are OK making a physical and visual change to your vehicle, you do what you can to make a better antenna than what was provided "OEM" by the manufacturer. Consider that the OEM radio or entertainment center was built as an integrated system, and changing the antenna might not work well with the OEM radio.
Back in the old days with an analog FM radio in a passenger vehicle, the radio person would mount a 1/4 wave whip at 100 MHz right in the center of the car cabin roof and make a solid connection to the metal roof for the coax shield. These days, nearly all vehicles have a disguised antenna that has compromises this group knows well.
