I have spent some time to find a working solution and the right settings is pretty surprising to me. My clients were ignoring the AiMesh node even with RSSI -80 dBm on 2.4 GHz band. Long story short. Once I set up 80 MHz channel bandwidth on 5 GHz radio, it started working as requires. It means clients on weak 2.4 GHz signal got reconnected to 2.4 GHz stronger signal of the AiMesh node. I have no idea why it helped but it works so for me.