It is not possible to set the width and height of a region attachment in the Spine editor. It always uses the width and height of the image file. The only way to change the size of a region attachment is to use scale X and scale Y, but that is based on the size in the image files.
If you use data import with scaling, it's expected you provide appropriately sized images.
Note that meshes are scaled when using data import. For meshes their size as attached on the skeleton is not defined by the image files, it is defined by its vertex positions.
