If I may ask a question:
I watched the practice, and loved the flow of the attacks, but the defender movement seemed disappointing to me. Looking at the video the defender rarely moves out of the line of attack, and almost never moves forward. I don't see any Irimi or Tenkan, not to speak of other tai-Sabaki.
I only glanced over the explanation, perhaps this type of movement backwards is an intentional limitation on the practice, if so, please explain the reasons for it.
Thanks for your clarifications.