Anywho, in my research I discovered the following article from February 24th, 1940 from The Miami Herald. Sure, the headline identifies it as a story about G.I.s in France wanting to hear the broadcast, but that's most likely an overzealous editor attempting to drum up interest in a war America would soon be involved in.
As you can see, the article is about the early spread of the Ranger's program thanks to Trendle and company's identification of syndication and original programming (which they continued to own) as the business model with the biggest payoff. Notable too how big a part of the Ranger's success Fran Striker's scripts were and how the station managers gave him credit for it. I'm not really sure what's up with that last paragraph though.
For more info on WXYZ's Golden radio years, check out this great tour of a former Michigan Historical Museum exhibition on radio's history in the state.