The three π loudspeaker is rated for quarter-space because that is how it is designed to be used. However, the raw Delta 12LF driver was rated in half-space and there is 3dB difference in the two.The one π, two π, two π tower, three π, four π and eight π loudspeakers are rated for quarter-space.
The five π, six π and seven π loudspeakers are rated for eighth-space.
The 12π hornsub is rated for half-space.
These radiating angles were chosen because that is the way each of these speakers was designed to be used. Of course, the 12π hornsub will usually be used in pairs or groups. That increased output by 3dB for each doubling of cabinets, if total electrical power remains the same. When voltage remains constant, there is 6dB increase when the number of cabinets is doubled. If placed against a wall, add 3dB. In a corner, add 6dB.