How to force device (in my case licznik_energii: SPM02 ) connect to stronger signal Zigbee router?
Whatever I try it always connects to coordinator with LQI: 30-70 while it has very near plug gniazdo_b) with ~160 LQI
PS Ive tried to select permit to join gniazdo_b only, but it connected again to coordinator
Zigbee does it’s own thing. Even if you convince a device to connect to something, it will find it’s own route when your back is turned.
Not good 
Should be really an option to indicate device connection prio, or at least option to unbind from selected router
Radio propagation seldom works the way you think it does - even second to second. The strength of mesh networks like Z-Wave and Zigbee is they are dynamic, and don’t get configured by hand.
Add a few mains powered Zigbee devices in the area, and let the tech do it’s own thing, and read this…
Thanks.
But (as you see on my pict) I have 5x mains near this device and only 10 other devices…
Dont know why SPMN02 do not select [2] which is 50 cm away but [1] which is on the other floor…
Usually, I see a No user serviceable parts inside sign as a challenge, but mesh networks are an exception.
If there’s high latency (delayed by noticeable amounts, not 200mS), you might check for interference. There could be foil-backed insulation, metal pipes, a poor firmware implementation, and a hundred other invisible factors. Adding more mains powered routers is always good, and can also reduce battery usage.
Without debug firmware or other specialist tooling, you’re only torturing yourself.
Zigbee 'aint BGP! 
I can confirm this - sadly many devices do stupid things and it’s not possible to change.
For me it was too much and I changed all ZigBee devices for ESPHome WiFi devices which can be maximum controlled. Even local routines are easy to implement - a huge difference when used to the ZigBee walled garden.
But also something much harder for non technical users to do. Home routers are really reaching their limits now - which is why I am delighted that matter is an IPv6 technology. Just because a home router has the possibility to hand out ~252 addresses, it doesn’t mean it is capable of managing ~252 addresses.
You are confusing the difference between the router handing DHCP leases - which for home routers on a Class C private network (192.168.0.x) can only be 192.168.0.1 - 192.168.0.254 but often especially on the WiFi side of the router, they can’t actually handle that many connections. With the Router’s state table, which is the router remembering the state of every open connection, which is necessary so that incoming data can be sent back to the correct IP address on the network that requested the data. By the way the fact that your router even tells you about the utilisation of the state table, the memory utilisation and the disk space utilisation immediately puts it in a different class of “home router” - because traditional ISP supplied routers, simply don’t expose any of that information. Many of them won’t even let you change the DNS servers.
