As I said, I presume that when Flugprestanda enter the performance criteria (factor) for each column, the 0 wind speeds are worked out for optimum performance whereas the 10kt tailwind speeds are calculated for minimum required performance.
I would consider this unlikely, the input parameter form allows for multiple wind columns, so all of the other parameters
should, remain the same.
Note to anyone from Flugprestanda who is reading this, its time for you to have a Q&A section on your website!
Mutt.