BMW has a specific warning about only tightening bushing hardware when the cars weight is already on the parts.
The reason is exactly what you stated.
Never tighten suspension bushings until you are at static ride height.
The bushing is always going to want to return to it's "at rest" position.
Example: Grab your right index finger with your left hand firmly. Now move your left elbow up and down. Your finger is always going to have less stress on it when your elbow is at the point where you first tightened your grip.
