I live in a house with two floors, upstairs i've got my ISP Router connected with a coaxial cable straight that comes straight from the street. As the wifi signal downstairs is too weak, i decided to get myself one Deco, my idea was to install it downstairs, by passing an ethernet cable straight from my ISP Router to my Deco. I managed to install it like so and set up my Deco. Problem is, that when i go upstairs my devices do not connect to my router and still remain connecte to the Deco. The behaviour that i pictured in my head was what the mesh is marketed as: when i get closer to a device with a stronger signal, connect to it. 

I want to know if it is possible to achieve this behaviour with the described setup, having my ISP Router act as a Deco, constituting a mesh of a total of 2 devices. I tried changing the Deco SSID to be exactly the same as my Router upstairs, without success. Also i tried enabling Fast Roaming and various other things. 

My knowledge on networking is very limited, i'd be incredibly thankful if i can achieve the desired behaviour.

Thanks in advance, Ramiro.