Here is my “local” area.
I’m the piaware south of the planeplotter (red) at Valencia. He’s included in my nearby ADS-B sites but obviously cannot MLAT yet. The other sites are east of me on the coast, west at Albacete, and south at Murcia. Since Murcia only operates about an hour a day he doesn’t figure as part of the MLAT sync much.
So, I generally see I’m synced with two other sites, those either side of me. Why don’t I sync with more? Agreed, I think both sites on Mallorca are off line but why not the site a Tarragona? I see a/c from Murcia all the way up to almost his position. He’s online now, so we should be seeing the same traffic, plus there is a clutch above him and they should see the traffic too. They show good MLAT figures so why no coverage with me? The same goes for those north west near Madrid. I see traffic descending towards them until ~25k near Cuenca. We should all have overlap.
If the answer is signal quality then I’ll try a better antenna and, once my connectors arrive, an amp to try improving.