The X property specifies the x offset, in pixels, of the upper left corner of a window if a new window is created. The offsets ...

The X property specifies the x offset, in pixels, of the upper left corner of a window if a new window is created.  The offsets are from the upper left corner of the screen.  For GUI processes, the specified position is used the first time the new process calls CreateWindow to create an overlapped window if the x parameter of CreateWindow is CW_USEDEFAULT.  Note, X and Y cannot be specified independently.