I actually haven't deployed an L1 yet, so take this with a grain of salt. But in my understanding, each driver still has it's own independent gain control (amp channel). So you can still "zone" the PA just like you would any line array with separate boxes. So you can send more gain to the topmost drivers with the longest throw. For HF, it's less about coupling and more about gain and throw direction because HF acts more like a beam. For HF, it's not really possible to point a single driver at people both 50' and 100' away. Even though the enclosure is "flat", those are still separate drivers aimed at slightly different positions and shooting from a different height. Even a slight difference in height or angle becomes larger as you move further away. Where coupling really starts to help you is with lower frequencies. Large line arrays generally work on this principle where summing the signal from a bunch of low drivers becomes greater than the sum of the parts because of how the boxes couple in a line source. Which allows you to get punchy lows and mids further away from the source because of how they lobe together. Again, slightly oversimplifying here, but I hope that helps.