Well as so often Geddes talks a lot of bunk. In a very live room there is probably a merit to wave guides. For most HF units I believe it is a detriment.
My in wall is wide dispersion by design. It has to be as it is a huge space, and I often listen right out in the kitchen and it has to sound fine everywhere.
You can see my in wall is very wide dispersion.
Above all it has good dispersion in the speech discrimination band, which is crucial, especially for a system that is only for music system a small percentage of the time. Good speech is essential over a wide listening area in a system like that.