I have three Decos for my home wifi in my long apartment—one X10 (the main Deco) in the Living Room at the front of the apartment, an M4R in the 'Second Bedroom' in the middle of the apartment, and another M4R in the 'Main Bedroom' at the back of the apartment.

See above for the current map of my mesh. I want to force the Main Bedroom Deco to connect to the Second Bedroom, not the Living Room, which is further away. Sometimes it does this automatically, but then if something gets interrupted, it reverts to this set-up, which doesn't work well. 

Can anyone help?