Running a single whip on the grab bar behind the cab will out perform an antenna mounted on the bird perch and running co-phased. The single whip will have better TX and RX since a true co-phased system needs to be a minimum of 9ft apart or the antennas will radiate in a figure eight pattern and reflect off one another. I have no problem talking over 20 miles and some nights with good conditions I've hit over 40 mobile to mobile. My RX is absolutely killer and I will hear and talk to stations that guys around me can't hear. I get asked every night "what kind of radio are you running...?" and "I can't hear who you're talking to."