I've no experience of using the Impression series, which seem to combine both absorbers and diffusors.
They come in different patterns so my guess is that the linear patterns (Digiwave, Gatsby, Mod Geometric)would have different effects if vertical or horizontal but that the other less linear ones would not.
You should also ask about the distance of the diffusors from your ears when listening as they require a certain distance for them to do their work (the QRD diffusors for example require around six feet I believe).