Yoshigasaki Sensei explains here how the bokken is conducted at shomenuchi and how to retreat with the bokken in tsuzukiwaza 30.
When retreating in chudan kamae, the bokken is not taken over the head at the end. The bokken only goes up if you go forward. While the step forward is set, the bokken is also led upwards.
"This is the logic of space, form and the relationship between body and bokken. In the real world, you have to be aware of the space."
The recording was made in Turin.