Here is a 3D mock-up of my design to the scale 1:6. I have explored the layout of the threads running between the entrance and exit to form the tunnel. My aim was to force the tunnel to decrease and then increase in height so that people had to duck as they navigated their way through it. Also, this would visually create additional length to the tunnel as it would add lines of perspective.
I experimented with allowing the threads to cross by staggering them to create fixed points, where the tunnel became narrower. Unfortunately the construction of this caused a large section of the exit to become blocked off and having multiple points of perspective resulted in some of the depth to be lost.
I have amended the design so that it creates a natural parabolic curve and focuses on one central point of perspective.