I mentioned three frequency ranges where arrays act differently. One is very low frequencies, where all drivers in the array are within 1/4 wavelength of each other. The next is where adjacent drivers are within 1/4 wavelength, but the array length is greater than 1/4 wavelength. And then the next is when each driver is further than 1/4 wavelength from each other.

There are also room interactions. The floor acts as a reflector, so your lowest driver acts like there is one below it, twice the distance to the floor. The whole array is mirrored that way. The array's directionality at high frequencies tends to mitigate this, but as frequency goes down, it becomes more apparent. And if the array is positioned too close to a side wall, that will reflect it too, acting like a horizontal array.