Somewhere along the line you are changing the scale. Do a search on "Poser Morphs" and you'll find various posts on maintaining object scale through the construction of a morph. First off, both Carrara and Poser automatically scale imports unless the check-boxes are unchecked. They also have option to move to center of scene (which you also do not want). Oh...and of course the actual prop can be scaled and translated, just as long as the base obj file for both the original and the morph are exactly the same size and position. Something I've done more than once (to solve a scaling mistake); import both your original and your morph into Poser, switch to Wireframe view and Ortho camera, and adjust by hand until they line up. It isn't perfect, but it can often be enough. (Then, of course, export the morph as a new object file).