Please see this post. Also, in LoRaWAN, not having sufficient separation/distance between sensor & gateway is a problem - this video shows how to measure this.
In my experience, even given a challenging environment (lots of metal walls, many layers of rebar-concrete, long distances, heavy EMI, industrial manufacturing facility, etc), when one uses only quality OEM antennas from proven vendor (Laird, Semtech, Murata, etc), LoRaWAN is so incredibly robust that two gateways are plenty (really for redundancy purposes, as one is on WiFi and the other wired Ethernet ).
I was spooked reading about poor RSSI/SNR and assumed the worst, so procured six gateways. but have installed only four and I find that my link budget is very good even in worst-case. So, I am planning to scale it down to three and keep the fourth installed but off, as a ready-spare.