I should think that the distance between those tweeter will give you a huge problem with comb filtering at only 12 feet. I have a PE neo's that I cutting to the core edges to avoid the coming at least out to about 18Khz, well beyond my hearingI should think you have some combing already. Also running them that high you probalby need to tapert too.
But I refer to people like Jim Griffin who are the real experts here.
eric j