It is important to consider the dispersion angles, or coverage, of each loudspeaker, and ensure that at the point at which you are at the extreme of the loudspeaker's horizontal coverage angle, you are overlapping with that from another loudspeaker, to prevent "dead spots", areas where the high frequency sounds from the loudspeaker drop more than 3dB below those on axis of the loudspeaker. This would reduce the speech intelligibility and the clarity of the music reproduction.
Cuboid 3 horizontal coverage
2x Cuboid 3 positioned to overlap horizontal coverage
For Cuboid 8 and upwards, the horizontal dispersion is narrower, and the loudspeakers will necessarily be placed close together, or further away from the listeners for seamless horizontal coverage.