When stamping using position and justification:

Set the position, justification and scale parameters. Coordinates should not be specified for the stamp item.

When stamping images with coordinates you can specify the size one of two ways. Position and justification parameters should not be set when stamping with coordinates.

Specify the bottom and left coordinates and a scale factor. The default value for scale is 1. You should not specify top and right coordinates when using this method.

Specify all four coordinates (top, bottom, left, right). The image will be scaled in the area you specify. The scale factor is ignored.