If I anchor a sculpture in a specific location, will the QR code ask users to reposition it?

to my understanding, there is no way to do exactly what you describe. You only have 2 options, and there are pros/cons to each.

Option 1: allow your user to place the sculpture on any horizontal surface

pro: user can physically move around the sculpture, get close, etc. and it will stay in place (nice experience for art)

con: the user can choose to place your sculpture on any horizontal surface they choose

Option 2: use an image anchor

pro: You can physically place the anchor image on the pedestal, and your sculpture will only appear on that spot

con: you have stated that there is no image to anchor it to, I just want to be clear, the anchor image is something you create and physically attach to the pedestal, so it can be a photo of the art, or your logo, anything. Just want to be sure you understand that part.

bigger con: if the user tries to get close to the sculpture and the image anchor moves off the screen, the experience breaks, and the user needs to bring the image anchor back into the camera's frame to see the sculpture again. (very disorienting)

An almost workaround: You could choose the any horizontal surface option, and have instructions physically posted on site (perhaps signage) to tell the user where to place the sculpture, and hope that isn't too cumbersome