I still can’t get my head around the fact that multiple beams are visible but only one is doing damage. Surely the others should be hidden. Of course, that would make it look as though the single beam were flickering around outside the player’s control - but then that’s what’s really happening, isn’t it?
The other beams are dealing exactly the same damage as the middle one (in case of 3 beams), just not on the same target. Only one beam can deal damage to any given target at a time, while the other beams are doing the same to other targets. It’s extra AoE, not extra damage.