I think what the other commenter meant to say is that you should use the gross contributions.
If A contributed €80 and took out €100, while B contributed €100 while taking out £80, the net contributions are
A: -€20
B: +€20
Now if €90 euros (50% of the current contributions) are to be raised for new spending, it would be strange to assume that all of it will come from B because they are the only ones with positive contributions. If we go by proportionality, it would make more sense to increase contributions to
The EU does not have 800 billion to spend on this, the money will have to come from the contributions of the member states.
I think what the other commenter meant to say is that you should use the gross contributions.
If A contributed €80 and took out €100, while B contributed €100 while taking out £80, the net contributions are
A: -€20 B: +€20
Now if €90 euros (50% of the current contributions) are to be raised for new spending, it would be strange to assume that all of it will come from B because they are the only ones with positive contributions. If we go by proportionality, it would make more sense to increase contributions to
A: €120 B: €150
ah yeah that makes sense