It is because the bounding box is based on the actual wcs .
I was thinking in a option to get length , to get the volume and according to section area to get it.
Of course it will need to add to the layer name the section area value like "Angle Brace - 0.9375" so when you pick on it the area can be get and then do the calcs to get the length , of course there will need to add some volume as the bar´s end are cut to fit the others ,