scale invariant "shapes_residual"

Thanks for your great work, help me through the paper. But there is still one problem confuse me.
In matlab code, i found you transform the intermediate's "shapes_residual" to the "meanshape_resize" coordinate system, while the latter's bounding box is exactly the same as intermediate's shape. Which means the "shapes_residual" would depends on the image resolution, e.g. same image, if i double its size, the "shapes_residual" would be doubled, and the binary feature still the same. Would this affect the global regression? Why not just transform to the unique param's "meanshape"?