How do you properly set up a horn speaker

I have Classic Audio T3.3s, very similar and have good results with them only a few inches from the wall behind them. I find it helps to have them toed in to the listening position.

I recently moved, in my old room I had the speakers close to the rear wall there as well and imaging was spectacular. At shows John Wolff and I have often set them up fairly close to the rear wall if the room was small. I think the best sound we ever got was at the Munich show three years ago; in that room Purist Audio had a program that did the speaker placement and despite very little in the way of room treatment, it worked quite well.

In a nutshell they don’t seem to be picky.

So for more of a 3d sound would closer to the rear wall or further out in the room be better- according to cardas- I should have the speakers almost 7 feet out into the room????

I have no experience with your speakers but at the risk of stating the obvious, do what many of us do and have someone or two move the speakers as you listen and let your ears decide which placement is optimal. Every room is different.
Good luck.

So for more of a 3d sound would closer to the rear wall or further out in the room be better- according to cardas- I should have the speakers almost 7 feet out into the room????

Like I said, I've had good success with my T-3s only 6 inches from the wall behind them. I don't think you need to worry about Cardas. The horns are helping you out here.

Cardas placement has to do with speakers that act as omnisirectional sources, as pretty much all dynamic driver speakers do to some extent up to about 9KHz. Horns don't really act like that. Horns aren't really wave guides. They're compression transformers. They lose their effectiveness once the size of the wave exceeds the dimensions of the horn mouth. That tends to make them vastly more directional than a dynamic speaker and allows for much more liberal placement. Cardas is intended to avoid boundary reinforcement and effects. You can't really reinforce a horn with a room unless you're using part of the room as the horn, like the Klipschorn.

At least that's my understanding of the things...