Compare the model leverage plots below. In the first, the x-values are being offset from their actual values, which is not happening in the second.
The only difference between the two is that I've changed one number - table attached. The 214 in Factor 2 become 185 so that the two leftmost and two rightmost x-values in each plot are equal.
From reading the help guides I'm guessing the offset is something to do with the increased mean, but I don't understand why this affects the points in Factor 1, nor why the two leftmost points of Factor 2 are offset by different amounts (one +ve, one -ve) when they are equivalent. It seems to be artificially improving the model.
Any help that can be offered is much appreciated.