Half wave mobile antennas

[bad boy]

I talked to one of the dave made techs and he said the rod of god was made for the back door to be isolated. that's hard to believe because if the back door is not grounded, how would the rod know that its back there. you have to have a neg. and a positive to react. the grounded back door, kicks the rf forward again, hitting the rod and increases the db gain. will some one explain this theory if its true