Range heavily depends on the geographical situation and the environment. If tall buildings or trees are in range, it impacts your device.
Also far distance mountains blocks it.
Finally some electronic interferences in your area also do have an impact.
This cannot be fixed with changing antennas only.
What you can also try it different values for gain. Setting it to “max” is not always a good idea.
install the graphs from wiedehopf and monitor it for some days.
The number of messages larger -3dbFS should not exceed 5%. If you are getting close to that value, you have it optimized.