Mr. D,/ Erik,
Yes, it is true that design must be involved for the proper flare for a given driver, and because of that, I am stabbing in the dark at best.
What eluded to this thought was in reading part of the ’Getting Better Sound’ by Jim Smith. I do not agree with every thought that Jim has, yet, there is inspiration here and there. In this case, he mentions the directivity of some driver designs (horns, I bet) that encourage less reflections from side walls and other room boundaries. I had an old set of such horns lying around that I have experimented with years ago. Even though there isn’t perfection to be had, the application has one desirable effect. The dispersion of the drivers is more spot on, and maybe even to some degree matches better the sound of the drivers rear loaded horn design to begin with. When the novelty wears off, I may well have other things to conclude.
Erik, likely I will be encouraged to look into kits as well in the future. These short horns are maybe 2 1/2" deep with a fast flare after the first 1 1/2". They are the diameter of the cone area which is 5 1/2". I will try to seal around the edges since I am sure it would have a different effect.