Background:    

Some users might notice that all satellite Deco units are connected to the main Deco, instead of the nearest satellite Deco.

Typical Layout:

Why does the satellite Deco still keep selecting the main Deco as a signal source instead of the nearest satellite Deco?
Deco will choose the best signal source by itself. The selection does not depend absolutely on the signal strength, but also on the connection rate.  Sometimes satellite Deco units may get slower speed due to half-duplex mode and interferences caused by connected devices like phones, or other devices.  To ensure the satellite Deco gets reliable speed, the main Deco stays selected by Satellite Deco after comparative analysis. 

Some users tested that after moving one of the satellites far enough and not being able to reach the main Deco, they finally get the desired connection map:

However, the speed of the satellite becomes slower than what it could get when connecting to the main Deco directly.  Due to the working pattern and protocol/regulation of Wi-Fi technology, the more wireless hops, the slower the speed would be. This rule applies to any kind of mesh or extender system. So it is not always good to connect to the nearest Deco unit.

Solutions
Deco Firmware Updates Adding Signal Selection and VPN for Multiple Models

Related FAQ:

How can I find a suitable spot for my Deco?