The events ANITA recorded in 2007 and 2016 are interesting data points. The question posed about how deeply cosmic rays penetrate into the earth is tied to this. As you wrote, the ANITA events happened during solar minimum. A time when the earth is less protected from Galctic cosmic rays. I believe ANITA didn't detect cosmic rays originating from within the earth, but rather cosmic rays passing through it. Answers the question of how deeply cosmic rays can penetrate. Answer being fully, through and through.