That is in fact, a fact. But if you have freedom of placement(assuming this is true if you’re placing duals already) you can definitely get a nice smooth response. Might not be perfect, but you should be able to do very well if you can place it where it needs to go. And with multiples, it’s just the law of averages in that the more subs in the room, the better the odds are you can smooth out the FR. The back side is that it’s no guarantee, and in Fact you still have to place both subs in a dual configuration for best results, and without that, it can absolutely make the FR worse.