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This will actually be a separate cube shaped object in your scene, which can be manipulated like any other object (translated, rotated, scaled). The volumetrics will be visible only inside this cube shape. Please see your plugin documentation, for specifics on how to add a Constant Density object to your scene.
An example mimicking heavy atmospheric haze using the Constant Density cube encompassing the scene, and the result renders with/without the volumetrics. Note that a very low density of 0.003 was used since the Constant Density area was so large in this case (1km). The Maxwellsea extension was used to create the terrain.