Where I grew up, it was only possible on the best radios to hear WLS 890 when WFDF 910 was on the air until 12:30 AM. There was a place where you could hear WLS 890 and WOKY 920 in the Daytime, at a receiving location in a null a few miles away, on a Delco car radio. The three towers for WFDF were located at the SW corner of Bristol Rd. and Howe Rd. in Burton, MI from 1941 until 2006, when they moved to an 8 tower 50/25 U4 facility just North of Carleton, MI. Right across the street, off Bristol Rd., was/is a Subdivision called Radio Acres. The street in the Subdivision was/is ironically named "Ellis Park Drive", where the WFDF signal was well over 1 volt/meter Day and Night, and WLS could never be heard while WFDF was on the air.
So in the outlying areas in the nulls generally to the South of the local Top 40 stations, the signal of choice was WCFL 1000, which was much stronger than WLS. As I measured with a real FI meter, the WCFL skywave signal maxed out around 10 mV/m. Due to the 190 degree WLS tower, the vertical radiation characteristic was less than WCFL's various circa 180 degree towers, and the IDF was much higher in the near maximum 80 degree azimuth direction. I never saw any ratings which included WCFL though.