Distance between DR bucky stand and X-ray machine

Someone bought the DR bucky stand. I would like to ask what is the distance between the DR bucky stand and the X-ray machine when filming?
The DR bucky stand should be placed on a flat hard surface 180cm away from the X-ray machine, so that the vertical center of the DR bucky stand’s film box coincides with the center of the X-ray machine’s emission rays. After the adjustment is correct, you can shoot. If you are using a mobile DR bucky stand, be sure to fix the DR bucky stand. When installing, make every effort to keep the vertical center of the DR bucky stand consistent with the coincidence of the X-ray machine, otherwise there will be a phenomenon that one side is bright and the other is dark; make sure that the distance between the DDR bucky stand and the X-ray machine is about 180cm to keep the film clear Degree and radiation damage caused by too close exposure.