If you’re asking about range, you’re still thinking of Zigbee in terms of point-to-point messaging.
A stable Zigbee mesh blankets an area with connections. Devices should be able to adapt to changing conditions by changing the routers they link to - you can’t force them to make any particular connection. One router (however close) may work some of the time if you’re lucky, but as you’ve found it may not work at all.
LQI and RSSI values can be useful to give you an overview of how a network is performing, but they change all the time (set up an entities card and have a look).
With the ZHA integration at least, the network “map” is a snapshot of all possible connections, not just the ones that are being used.
Lots of good advice here.