Yes it is possible. It is just a matter of where you place the boxes in 3D space relative to where you placed the image. From what you describe, you placed them below or behind the image.
Try orbiting out of plan view to get a look at where things are located in 3D space. SketchUp is a 3D modeling app, and sometimes viewing directly along one axis, particularly in parallel projection, can mislead you about where things are located.