Hi,
in past I searched everywhere, finding nothing about the usage of MIMO systems with different antennas connected to the two (or more) chains.
But, as I am electronic enginner as well as wisp, I thought that more than one antenna on different chains would behave as they are connected to one single radio with antenna splitter (as in television broadcast TX systems): a complex radiation pattern with one single channel used.
I tested it now in more than 4-5 public installations with lot of success: using one single 2,4 Ghz with two sector antennas allows create "front and rear" and "180° sector" coverages without troubles deriving from nearby radio interfaces on two different channels fighting among them with mutual interferences.
I reached 50 wifi users on the same basebox ap in a site similar to picture I attached, all surfing web happily!
I make this post to help anyone would search infomation about MIMO used this way.