The Scaleheight of Giant Molecular Clouds is Less than that of Smaller   Clouds
  We have used an antenna temperature thresholding algorithm on the Bell Laboratories 13CO Milky Way Survey to create a catalog of 1,400 molecular clouds. Of these, 281 clouds were selected for having well-determined kinematic distances. The scaleheight, luminosity, internal velocity dispersion, and size of the cloud sample are analyzed to show that clouds smaller than ~200,000 solar masses have a scaleheight which is about 35 pc, roughly independent of cloud mass, while larger clouds, the Giant Molecular Clouds, have a reduced scaleheight which declines with increasing cloud mass. 
Antony A. Stark, Youngung Lee