Sima BIrach also owns WCXI 1160 Fenton (30 kHz from WDFN 1130) and 770 WTOR Youngstown, NY (Toronto, ON) (30 kHz from CFZM 740). WNWI 1080 Oak Park, IL is 30 kHz from WXES 1110 (recently WMBI), and WMFN 640 Peotone, IL is 30 kHz from WSCR 670. Squeezing in 30 kHz separated stations into large Metropolitan Areas is the defining Birach move. In the US, the 25 mV/m contours of two stations 30 kHz apart is the restriction. I'd have to look at the Agreement between the US and Canada to see what that restriction is.
Looking at a few applications, there does not appear to be a 30 kHz restriction between stations in the Agreement between the US and Canada. The application for WTOR 770 shows that there is no overlap of their 15 mV/m contour over land with CFZM 740 in Canada. It just reaches the edge of Lake Ontario. But any requirement seems to have disappeared from the Agreement.