Hi Crab453 and welcome to the Forum. First and most importantly of all, it sounds as though you're using the discone (a very wide-bandwidth design of antenna - fine for scanners and higher HF frequencies) which just will not give the RB the 1090Mhz signal that it needs. Try getting out in a car with lap-top, RB and standard antenna, you may be gob-smacked at what you see!
With standard supplied antenna, I get up to 250nm out over the Atlantic, but I'm in the fortunate position, living on top of cliffs with clear views to the west and sw over the sea, with antenna at about 215' asl., depends whether the tide's in or out!
The third/forth screenshots have some rather gory colours, but is clearer to see the radius and distances, achieved with AN's supplied antenna which is a superb design, but let down by less than great construction quality, sorry to harp on AN, but this still needs to be addressed.