Clem & John,
Um, well, it actually can work.
Just as a lark, I did exactly that with two remotes using two engines. It yielded 10's on both remotes, however, I have no way of knowing if that's because the tests actually yielded 10's or because each remote was counting its own packets as well as the other remote's.
For anyone who's interested in learning more about the DCS signal and exactly how the test is carried out, please refer to The DCS O Gauge Companion 2nd Edition, page 55, DCS Signal Strength.
This and a whole lot more is all in MTH’s “The DCS O Gauge Companion 2nd Edition", available for purchase as an eBook or a printed book at MTH's web store!