Why? Well Rob, for a technical answer you will have ask some one else.
But for many years around here, the guys that wanted to talk long distance dx, always kept the antenna in "V", the antenna showed a stronger signal in the horizontal, then when mounted "L".
That's the only reason that I know why......
As an L it would be vertically polarized and as a V it will be horizontally polarized. Horizontal antennas benefit from an additional 5-8 dB gain from ground reflections that vertical antennas do not.