What I got from Yogani's instructions is that it doesn't really matter how specific the tracing is and that the main thing is to get from the root to brow to root tracing the spinal nerve where you feel it is.. he also says that in time we experience the spinal nerve and its location..
here's a quote from the pranayama book:
quote:The main thing is that we end up at the brow at the completion of inhalation and at the root at the completion of exhalation. How we get back and forth is less important than traveling from one end to the other without strain during our slow deep breathing. In time, it all comes together.