If everyone on the planet picks one address in a 256^12 namespace, there is a 1 in 9903520314283042199 chance that you pick the same address as someone else.

Choosing the same topmost bits as it hears in other stations in the area and always changing only the bottom 2^bits~=9903520314283042199 just to maintain the absurdity of it; less would work too, like one in a million if that's even more advantageous to performance for some reason.