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Probably you and I are the only ones left reading this thread, Ermi, but I thought you’d be interested in what John Kraus says on this topic.
The link below leads to a scan from Kraus’ Antennas, 3rd edition. His point that two of the fields cancel at the radian distance was interesting.
Agreed that the region boundary can be considered arbitrary, although Kraus and Balanis both use the same 1/2*pi value for it.