Thanks for your reply.
I think I should have been more precise in my original question. The system makes sense to me conceptually, what I don't understand is why the length is 128m and not, for example, 200m or 100m. The maths of it is the part I'm struggling with, I think.
I've recently been reading this paper (a free version is available here).
I've been trying to work out how they came to the 128m length, but I just can't. Feel like it's been just beyond my grasp for a long time and it's been driving me mad. Any help would be appreciated.
Thanks in advance.