@akinomeroglu 

Devices should not roam back and forth so often, you may have different issue you are trying to fix the wrong way.

Answering your question: it is not possible to reduce signal on one Deco unit through Deco app configuration.

Still, wrapping X50 in few layers of aluminum foil will do the trick. You can experiment with how many layers you'll need, also make sure you do not block X50 air vents. 

  @Alexandre. Hi

Thanks for your reply. Do you have any other idea why devices go back and forth and is there any other solution?

  @akinomeroglu 

I have different situation with my Deco mesh: devices that are stationary do not roam frequently. That makes sense: for smartphone to roam it must rescan WiFi networks to figure where to roam, that eats battery a lot. Smartphone software developers try to avoid it (unnecessary roaming) as much as possible.

I can think of two cases where smartphone will be forced to roam between Satellite and Main Deco:

1. There is an issue with power supply for Deco unit. When power goes off (even briefly), all devices connected to that Deco will be forced to roam;

2. The WiFi backhaul signal between Satellite Deco and Main Deco is weak. When Satellite Deco loses connection to Main Deco, even briefly, it will force all devices connected to it to roam to Main Deco. With power flickering you might be able to catch that, especially if Satellite reboots, but losing and regaining WiFi backhaul may go unnoticed.

When you open Satellite Deco page in Deco app, what does it say for Signal? If it is Weak, this might be where issue is.

  @Alexandre. thanks for your reply again. 

I checked my power usage (got some smart plugs which tracks usage.) There is not any chage on power usage so I assume that devices are healthy. They already connected via cable so I do not think there is a backhaul signal problem.

This problem only occurs for the device that I am taking from one room to another room and I can repeat this problem in 3 different cellphones, 2 tablets and 3 computers.