Clarifications on azimuth and elevation using a 2D antenna array?

[Jud-Ken-Do]

Hi, thank for sharing this amazing project.

1. I would like to ask you about how you are able to get Azimuth and Elevation using antennas from horizontal and vertical sides of the same 2D array?
2. Why horizontal => Azimuth and vertical => Elevation? Does it make any difference in a 2D array?
3. M=2, but you are using 4 antennas in the switching pattern. why not M=4?
4. Assuming we are trying to find only the azimuth angle, is it possible to use antennas from both horizontal and vertical sides?