I have a pretty lively ceiling slap in my living room. In certain places, you can hear kind of a ringing echo, only at very high frequency, sort of a pinging sound. You can even hear it when speaking. If I had speakers with a wider vertical pattern, it would be a problem because some speakers ring terribly in this room. But the narrow vertical dispersion of the horns I use completely eliminates it. No problem at all.This is one place that shows very distinctly how reflections from the room definitely contribute to the overall sound. It also shows how effective controlled vertical dispersion is.
Try putting your speakers in the corners of your room, angled 45° inward a la π cornerhorns. That way the radiating angle stays confined within the walls. It will reduce early reflections a great deal and may solve your problem.