How do you properly set up a horn speaker

They are treated no different. Horns are just waveguides (and yours are more like traditional waveguides on say a studio monitor rather than a true horn on like Advantgarde), and all they do is focus the far off-axis sound emission forward, giving you a wider soundstage and some added output.

Since Cardas isn’t asking your listening distance, it isn’t calculating for first reflections, so I would use the distance directly perpendicular to the speakers.

Some horns can be placed closer to room boundery then conventional but otherswise its like the setup for most loudspeakers consider radation patern and toe in if needed.

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.