A common denominator in this whole thing is the assembly location. I'd bet there is an issue with how the loader frames are aligned and tightened when installing them on the tractors. These were all assembled in either the Ohio or Florida service/assembly points after importing. It doesn't take much movement (misalignment) at a mounting point to reflect an inch or two difference at the bucket. It could be as simple as the order the bolts are tightened, if they are all tightened gradually, or how the frame is supported while assembling, to get a loader frame mounted square.