I’m not sure if this is normal, but I first added a UAT receiver a couple days ago (Saturday night) and would occasionally see a couple of aircraft on UAT using a really cheap antenna that came for free with a generic RTL-SDR dongle. I just received a 7 dBi antenna tuned for 978 MHz and was initially wowed when looking at SkyAware978… I had a quite a few more aircraft listed. I then realized that the majority of these aircraft were listed as TIS-B, including a Southwest Airlines plane coming in for a landing. Of traditionally UAT-received aircraft, the total is still just 1-3 aircraft at a time. I guess I am picking up a TIS-B ground broadcast, which is new, but no further-reach aircraft noticeable at this point.
Typical UAT aircraft are below 10000 ft.
Often range at that altitude is heavily limited by pesky geometry applied to the terrain (and to a lesser extent curvature of the earth at least close by).
Here is a rudimentary explanation to get your personal radio line of sight limit for a certain altitude.
dump1090-fa / skyaware support that json so i would assume skyaware978 does as well but you’d have to ask someone else on where exactly to put the file i mainly use the interface i’m coding on. (also i don’t even have 978, not in the US)
No amount of gain will beat a solid object in the way of 978 MHz / 1090 MHz.
Couple of trees or a single building you can sometimes get through with a high gain antenna and the transmitter of the aircraft not being too weak / far away.
But a hill or a dense forest or multiple or big houses … no chance.