That's true at my grand parents home in East Detroit ( now East Point ) WKNR 1310 could not be heard at night and downtown Detroit was ruff for it at night too. WJBK 1500 was alright when running 10k days and 1k nights but when they added the towers and power it seemed to be weak in East Detroit WXYZ did have a better coverage as their site is North of Detroit and the WKNR and WJBK sites were South. WIXY at Cleveland had a straight six tower array shooting North from south of Cleveland which pulled East and West in. WERE coverage was similar with no signal West at night. WYSL was running 250 watts at night until the power increase so it wasn't good more than 4.5 miles away from the tower site. The increase didn't help as they were on a channel ( 1400 ) that saw everyone else increase by the same amount so interference remained the same. .Could be. Both of the Detroit-side Top 40's had to combat 50 kw CKLW. Neither 1310 nor Storer's 1500 (and its collection of towers) could really cover the market.
Detroit, like Cleveland and Buffalo, were squeezed in between NYC and Chicago and none of them got a good set of AM signals. That meant that Top 40 did not always have the best signals. Look at McLendon's WYSL in Buffalo, WERE, WHK and WIXY in Cleveland, too.