Faulty logic
The military,commercial radio towers and cell phone makers want omnidirectional reception not directionality.
For these applications the user would have to face the tower, ship or plane to benefit from the higher gain. And radio towers would leave half the audience in a null and out of luck.
Two antennas co-phased can and do outperform a single antenna, it's called a phased array.
Co-phased antennas are by nature directional because signals that arrive at both antennas at the same time(broadside or forward and backward if the antennas are mounted on the mirrors) are added together and signals that arrive at different times/angles are not added because the peaks arrive at different times
If they arrive far enough out of phase/time they subtract and cancel each other out.
At ~18 feet apart (for CB frequencies) the signals that arrive from side to side cancel out and leave a deep null
This is the pattern as twin dipoles are separated from 2 feet to 22 feet.
the value of "sep" is the distance of both dipoles from the center point in inches. So sep = 12 is 2 feet apart.
The dipoles are at 0 and 180 degrees (12 and 6 o-clock)
