Horns: Why don't they image well?

My experience is that 'imaging' is not the sole factor of the speakers.

Everything in the chain will contribute.

For example...monoblocks will give a better image than a dual channel amplifier...all things being equal.

My highly modified Klipschorns suffer very little in direct comparison to my highly modified Merlin VSM. Hard panned information does 'stick' to the Klipshcorns a bit more, the Merlins seem to disappear with the same hard panned information. I think much of this difference is due to baffle width. The Volti horns are much better than the stock Klipschorn horn in regard to imaging. Center imaging is pretty much even.

Horns tend to give a wall of sound, but rarely can image pinpoint in the horizontal and vertical and depth like the above ones mentioned can.

This statement is simply false.

It may be true for some earlier horns as the throat design and curvature of the horn flare affect its response. These days that is optimized with CAD; horns can image as well as any other tech.

I own a customized pair of Avantgarde Uno's (pre 2006) that produce a wonderful soundstage...

As a follow-up to my suggestion above of horns imaging "differently," it's not meant to imply they do so 'per se,' but rather in comparison to a range of direct radiating speakers - I believe that's very important to point out. Really what it comes down to for me is the sensation of uninhibitedness as a desirable trait, and I gather imaging is if not irrelevant, then a part of the overall "equation" that comes to life largely via presence, dynamics and ease as something more substantial and dense in quality horn speakers; this, to me, typically imparts other terms of describing the sound as "imaging."