Its a good question. The Stage has been designed to either stand upright ideally against a wall or laid flat on say a shelf under the tv. The B&O App adjusts the sound profile of the stage to suit either position chosen.
My stage is currently laid flat under the tv. I purchased on ebay 4 sorbothane domes from ebay, so rather than the stage just sit flat on potentially a hard surface which could induce vibrations and colour the sound.
I have used the stage in both postions, laid flat and stood upright, there is a very slight and i mean very slight difference to the sound, its so slight i cannot determine which sounds better if at all. hope this helps . suggest you read up on user experiences on the beosound stage thread on this forum. The sound quality is spectacular in every sense we even have ex Ambeo owners, who have moved from that product due to issues they endured who are more than happy with the performance at more or less half the price.