I have a 2el yagi at 75 feet, and was listening to the EU on 20mCW, tonight. Made about 8 EU SSB contacts, and 3 US East Coast SSB contacts, from here in Seoul. (currently HL1ZIX) Even with 0 sunspots, and overall low numbers, greyline still works on 20m. My theory is that everyone is playing on FT8, despite SSB working.
The HF Oracle made her prescient prognostication on 3 September 2018, a week before that paper's abstract published date 10 September 2018.
Sorry Bonnie I did not check the dates. Perhaps they read the HF Oracles' prescient prognostication first then published their findings. Hi!