I have 3 x Deco P7. overall the mesh works well but with challenges sometime. my setup is fairly simple, I live in 3 floors house and I have my 3 pieces Deco each in a floor, the main one is connected via ethernet cable to my DSL modem in router mode.

The signal strength shows as weak even if PLC connection is established, my understanding that as long as the devices are able to communicate over powerline, so the signal strength should be shown as good. What can I do to improve the signal strength if PLC is already established ?

Sometime is more challenging as PLC connection between two of the Deco is lost and it is usually restored when I reboot the network (all Decos). I understand the best practice is to connect the Deco directly to wall socket with no power extension, are there any other recommendations ?

One last question, I am not sure if I understand TP Link recommendations properly, can I buy a new Deco on WiFi 6/7 and add it to the mesh I have ? I understand the powerline won't work with the new piece but will it work at all with existing WiFi devices?