All ADAM Audio studio monitors are specifically designed to be set up in a certain way. If not stated otherwise, the standard is vertical.
Of course, you can choose to use your vertical speakers in a horizontal position. If so, please make sure that the setup is mirror-symmetrical, i.e. that the tweeters both face either the outsides or the insides. This is crucial for a precise stereo image.
The A Series introduces a rotatable HPS waveguide and X-ART tweeter. This means you can rotate the entire waveguide and tweeter module by 90 or 180 degrees and continue to benefit from the HPS technology whether you position the speaker horizontally or vertically.