This does not apply to screens or curtains (or other objects other then fixtures). It would be great if as a general guide the bottom of objects keep their distance to the floor when resized unless they where snapped to another object, then to top of the object should stay at the heigth of the point to which it snapped on insertion.
Form objects (like Boxes, Curtains, etc.) should never end up half way below Y=0 on insertion.
When combined the two rules above should result in less actions on inserting and resizing an object.
Try with inserting a 'stage' (box) of 15 meters wide, 10 meters deep and 80cm high on floor (Y=0) level.