Select the top level node in the scenegraph (house) to select the entire model and look at the bounding box dimensions of the selection in the status bar at the bottom of the window. In this case the bounding box is [42.71,12.34,79.58]. The width value of 42.71 is similar to the width measured in SU (41.36). The bounding box expands to contain all geometry in the model and some of the trees extend slightly beyond the ground area.