Why do I use the zoom extents command in PostalCAD and have my workroom floor appear very small in one corner?

The typical reason is that you have an object that is very small placed far away from your drawing area.  These objects may or may not be visible.  Make sure that all OFF layers are turned on.  Sometimes the object may appear as a very small dot on your screen.  If there are no visible objects seen, zoom out a little and select the blank areas that might have objects. If grip markers show, you may want to open the Properties box to see what type of entities they are.  Use the OBJECT option of the zoom command to see the objects for closer inspection.  Move or delete the objects as needed.

Another object that can become part of the extents and not be visible, is blank text or blank block instances.  These two types of entities cannot be seen, so simply use the PostalCAD Erase Blank Text or the Erase Blank Blocks command from the Cleanup menu to remove these pesky little objects.