Remember what Kevtronics said about salt water. Fresh water is a poor conductor unless it has lots of conductive minerals in it. So stations along the Great Lakes just don't get much of a benefit from being next to water.The AM band radio signals carry a little further over water as opposed to over land. So to the extent the straight line path from the transmitter to coastal towns is over the ocean, the reception in those towns will be a little better than otherwise expected.