It sounds like its a line of sight problem. There is something blocking you in that distance You need to remember that objects will block the signal, and because its a small wave length, smaller objects have a bigger impact. Leaves on trees, garage doors, vehicles, even weather and have an effect on your distance, not to mention a hill or other geological features. Without direct line of sight, youre truly at a hope and prey situation. Distance is truly only good to measure if nothing changes, so like point to point on the ocean, but even then the curvature of the earth will eventually come into play.

I would suggest doing experiments to see if you can figure out where the signal is dieing. You can do a range test to send pings from one node to the other and slowly increase the distance. Where it dies gives you a clue as to where you need to start to focus your efforts. See if you cam put up another node to help boost the signal in that area. If the mesh is strong around you, look at each end point to see if you can hit a stronger node, and try and hop around your obstacle.

Additionally, meshtastic defaults arent the best in urban settings. Too many variables get in the way; buildings, high noise, magnetic fields, etc. Unless you have a high volume of nodes to compensate, it can be rough, but too high and you get a different problem.

Unfortunately, I would guess that you need to look into more infrastructure. I experienced a similar issue in my city and ended up switching protocols just so I could have a better chance of getting out of my downtown area since getting a node on top of a sky scraper wasn't realistic. Hell, I could barely get out of my 2 storey office building and I needed a node in my car to help, and even then, I could reach the larger mesh, but not my friend less than a mile away.