I have noticed that each day is a different experience with spinal breathing. The spinal breathing awareness and the energy that is felt sometimes travel from the root to the brow but sometimes it stubbornly travels from root to the crown no matter how much I resist it.
Some of it does go to crown by default, we are just advised to let that be and repeatedly favor the root to brow part. See http://www.aypsite.org/199.html
Simply amazing. I can actually feel the fork of the spinal nerve as forks off from the stem of the skull while performing Moola bandha now. I can only attribute this to refinement or the purification process as Yogani says.