In the mid to late 70's, I had regular reception of Dallas FM stations from Midland, TX and Lubbock, TX. Turning the antenna towards San Antonio and Austin from Midland, I could also easily get stations from those cities.
Since then, I have had regular 300 mile DX from multiple stations depending on the location. It happens when the transmitting station has high ERP off of a tall tower over relatively flat terrain. I suspect it is small nodes of signal that are created by the transmitter bay arrangement - creating little pockets of signal even hundreds of miles away. There was a Mississippi station that came in with a dipole in Altanta. Atlanta's 97.1 has a little node right at a gas station off of I-10 in Lake City. Absolutely reliable any time of the day, night, or year. I had some South Carolina stations coming in the car when I drove from Deland, FL to Daytona. Same station, completely reliable. Close to 300 miles. When I lived in the Dallas suburb of Plano, I could swing my antenna South and get 92.9 out of Houston - close to 300 miles given my location and that of the towers in Houston. I could swing the antenna around and get absolutely reliable reception on 92.9 out of Tulsa. And so it goes - little situations where DX from 300 or more miles was not only possible but reliable enough for regular listening. But because I could do similar ranges in the car, I really think it has more to do with the antenna bays and the moire patterns of coverage they create than anything else.
One reason I think this is that I did a show on a small low power station in Daytona Beach that had a very eccentric owner. It had a very conventional arrangement with a 900W transmitter, 350 feet of transmission lines, and about 4 bays creating an ERP of about 1800W. And in the fringes of its coverage - picket fencing as it got more distant. One day, the owner had a bright idea. He had bought a 6kW transmitter and absolutely insisted on using it, running it through a single bay. With transmission line losses and the efficiency of the single bay - about 2200W ERP, which was his licensed limit. Of course his electric bill shot way up and he abandoned the idea after a few weeks - but for that period the fringe reception was fascinating. When you reached the fringes, it was like the station dropped off a cliff. No picket fencing effect at all - just "there" or "gone". And it definitely went farther - a lot farther than the small difference in ERP would account for. So he was right - but for the wrong reasons. I don't think this would work for full class C, because the base transmitter power would be so high with corresponding high power bill, and running that much power up a 2000 foot transmission line would be problematic, as would finding a single bay that could handle 200kW+