Not sure about France wealth tax specifically, but the EU has always had a huge problem with taxes being uneven, especially stuff like corporate tax, with smaller countries "stealing" companies from the bigger ones.

This year a minimum of 15% eu-wide was introduced to stop the tax race to the bottom, something similar could and should be applied to a wealth tax.

Money has no value if you can run fast enough

The area is squared, so 1^2-(1/3)^2 which is .888 or about 88.8%

Having spent a good part of my life in the countryside, that's actually helpful