As we all know under Idea conductions a 1/4 wave whip will out do any
loaded antenna.
But in the real world a loaded antenna ( shortened ) mounted in the center
of the roof will work much better in ALL directions than a 1/4 wave whip
mounted on the bumper, or the rear of the mobile. If the long whip was
mounted on the left back side, the best direction will be to the right
front, whereas a center mounted antenna on the roof, even with its somewhat
more loss will work better in all directions, as the mobile would not have
to be turned like a beam. So the point is I prefer
a good trunk mounted, or a center mounted antenna over the 1/4 whip.

Been there done that.