It was a lot more than 5% of the yellow wall that was singing. And it was a significant chunk of that wall in the middle jumping up and down creating a great atmosphere. The periodic back and forth between the stands was also great. Credit where credit is due...
I don't think it is just down to our ground, most grounds are the same in the UK. We should be looking at clubs where it works and ask ourselves why.
Personally I think a large factor is the ability to drink in the stand and the ability to easily get beer around the ground at Dortmund that contributes to a buzzing atmosphere. All standing also is a factor because if you want a good position you have to get there early. Even the City standing area was packed an hour before kick off. People won't want to do that if they can't have their beer with them and take 6 in at a time like last night.
Of course there is a counter angle here, people with beer need to behave, especially in a standing section but maybe if people don't feel like they need to neck 6 pints before kick off there would be less problems.
Transport is also something we can learn from. Yup, I hear trains were crap last night, not the usual German efficiency expected, but bottom line it is free for most of them. Couple that with lots of free parking around, scooters to hire, etc, just makes it easier on people's wallets so they don't have to make a choice.
So maybe extend the north stand into a proper home stand with all standing, much cheaper seats, change the rules on beer and sort out transportation such that there is an incentive to stay or get there early.