What's the missing conclusion here, that the number of German standing areas have stayed the same in the recent past (indicating zero correlation) or that they've actually been replaced by seating areas in the more distant past (indicating a slight negative correlation)?
The problem with that is the rows in the north are already concreted, so it would take a LOT of effort to even slightly change the step spacings.
Other problems, transport is always an issue, toilets, and there might be evacuation problems unless more vomitories are constructed. Further to...
From my maths it's 66% increase, since an increase in the row depth of 20% will offer a doubling of the capacity as one person stands behind another. (ie. 2/1.2) That would increase the stadium capacity by about 3400.
I'm not sure where I got 1.2 from though, maybe that's rubbish.