Best answer by Airgetlam
OK, I had knee-jerked an answer, which turned out to be incorrect, my apologies.
If you look at the images of the Sonos device, it is designed, when mounted vertically, for the silver bar with the Sonos logo to be at the bottom. This is born out by looking at where the IR "reflector" is located, which is then at the top.
When the Sonos PLAYBAR is plugged in, there's a switch that determines what orientation it is in, and makes a modification of the way the speaker works based on that data. Note that you can't control that in the controller app....and if you plug in before it's in the wanted orientation, you can get it mounted, and then unplug and plug it back in, at it will reset.