Increasing the Upright Piano Distance from the Back Wall

 At your risk.

The back wall and the soundboard, 2 material surfaces of high area should produce standing waves in air.

Same thing with a grand piano between soundboard and floor. But the distance here is greater, creating a more open sound.

But it this respect the upright piano is more advantageous since the back of soundboard to wall distance can be made much greater than on a grand by for example placing the piano at about 90m degrees to said wall. (An assistance of many people should be used for moving safely the piano and avoiding injury. If there is skill the mechanism and other wooden parts lids etc could be removed in order to make the piano less heavy. using its wheels should help too.

Is it nonsense to have an upright piano close tro the back wall since half of its sound at least is radiated from the back of the huge vibrating soundboard?