Eh, what?

Radio signals don't deteriorate on their own. They spread (result is an inverse squared intensity falloff), and they are absorbed (exponential fall-off; for air, over any reasonable distance, negligible). No effects worthy of consideration fall off as the cube of distance.

The antenna suggested in the original linked article is rated as 14.5dBi. (A dipole, for reference, is about 2 dBi.) And you point out that other networks were about 30 db below yours; but if they're separated, and/or you use a directional antenna to reject the undesirable signals from your AP, that doesn't mean you can't access them. Without knowing the sensitivity of the receiver, and the reference power, those numbers are meaningless except to discuss SNR.

Edit: a half-wave dipole, of course.