even with 2 antennas mine always droppnig in and off... depending where you are relative to the nearest tv relay station, and where your dual antenna is installed, i find on my car I get better reception travelling east west, and worse reception travelling north south.
i know for melbourne we have a transmitter up mt dandenong in the east. and I live in the west. that probably explain why,
and my antennas are stuck on front and rear windscreens. i know there's a guy @ the meet who have the same antenna as mine (probably Chris Roger's unit) whose got his antennas mounted on both sides of the rear quarter windows. I'm not sure about which one is better, keen to hear from the owner of that car whether his reception is better or not.