Your spine naturally curves in at your lower back. At this point the spine is quite wide and thick. The front edge of your lumbar spine is a few centimetres in from where you feel it externally on your back. It is the front, internal edge of the lumbar spine, so within your abdominal cavity, that you want to place above your hips. Think of placing the point half way between your belly button and your back above your hips. (which are above your knees, which are above your feet)