You've just proposed a hypothesis, and it sounds plausible. Now, you have to come up with some experimental data to prove this hypothesis. So far, hams with hundreds of years of collective experience have stated that they have never (or only very rarely) come up with any data that would support the hypothesis of one-way ducting. There might be giant RF flap valve in the sky that we haven't seen. I would say that the burden on you is to establish its existence. This will be a great discovery. Get your license, discover it, and you'll probably get a Nobel prize.