A coil may steepen the slope but it also steepens the roll off vs. frequency. That is not what you want to do in my opinion as you would roll off the frequency far too much. EQ would boost the response and tend to flatten it across the upper couple of octaves which, to me, is what you should do.

Jim

Yes, that is the way to go in this case--use a crossover to a tweeter or a line of tweeters. I've found that simple first order crossovers (single component) aren't sharp enough for most line array implementations so a third or fourth order usually works better. Furthermore, the crossover likely will need to be when the midrange line starts to lose sensitivity. This would likely be in the 2-3.5 kHz area. Measurements help to determine specific crossover points.

Jim