@kasa_user 

Yes, I would set it on the 5ghz at -73.  That is a good starting point.  

on the 2.4, I usually start at -75.  

Just an FYI, you will need decent amount of cross signal to make this work at its best.  

  @kasa_user 

RSSI modification will force certain clients to move APs, causing some clients to disconnect from the old AP and join to a new AP. That is why you see this message in the log. To address the issue you pointed out, consider enabling fast roaming, which allows clients to transition between APs swiftly. You can also modify the remote AP's transmission power from high to moderate or low. As a result, clients away from it are unable to connect and instead connect to the nearest AP.

 

  @kasa_user 

I agree with hank... It seems like you may not have good overlapping signal.  

Load up inSSIDer on your laptop and walk around this area.  Confirm you have good signal and no dead spots.  OR low signal areas.  

  @kasa_user 

What is the device? Is this an IoT device?IoT devices may only connect to 2.4G networks and may not support 5G. Additionally, the device has its own mechanism for selecting a network.You can manually configure it to connect to 5G.Additionally, the device's network adapter could affect access to the internet.So, it presumably thinks the 2.4G connection is better.