connect station to mesh network

I have 4 units work as mesh
I want to take another unit that will move around and connect to the strongest signal
what do I need to config in the station unit to make it work?
I have try all the options but all the time I get

Tx\Rx Rate13.5Mbps/1.5Mbps
Tx\Rx CCQ - 93/56 %

if I make the new unit work as mesh - it work just fine ,so it not a hardware problem

so what am I missing?

Thanks ,