My Amazon Echo Dot can hear me from all four rooms on my main floor because it is mounted in the doorway. I can control all my lights and the TV without having to buy a second Dot, and it is out of the way with the wires concealed.
I bought a plastic wall mount on Amazon which looked nice but unfortunately it did not have a big enough cutout for the power and audio cables so I had to bore out a larger hole with my dremel. I would not recommend mounting a Dot on the wall because it would prevent the Dot from cancelling out background noise due to sound echoing off the wall which would greatly decrease its useable range.
20′ audio and power cables.
The audio output plugs into my ceiling speakers so I can hear Alexa from every room on the main floor. The Echo’s built in speaker would be muffled by the mount.