Thank you for feeding data. The airport surface coverage map simply displays ground positions received that are on the selected airfield. If you are able to see ground positions on the Dump1090 map, then it is likely you are contributing to the surface coverage.
In my opinion, I understood what was happening. One station has a large viewing area, but does not see aircraft below 300 meters above the runway. The second station has a small viewing area, but sees planes at the airport. At some point Flightaware began to prefer for tracking only one station with a large viewing area.