There is another factor that also impacts frequency response when using multiple sources, be they in a line array or any other alignment. The mutual coupling that occurs when you have sources closely spaced lowers the system's upper f3 frequency by a factor of 0.7 with every doubling of radiating plane area. While it's easy to increase average sensitivity by using more elements, the more elements you use the more response gets tilted towards the low end. The way to overcome this in large pro-touring multi-cabinet systems is to go two-or three-way, with the midrange section being more sensitive than the woofers, and the tweeters more sensitive than the mids. This way as more cabs are added to the array system response actually flattens.