Not sure if you actually meant logarithmic or exponential. An exponential tax rate would mean that the more you own the next unit of value would be a lot more in tax, while a logarithmic tax rate would mean that the more you own the next unit of value would be a lot less in tax. See x^2^ versus log~2~(x) (or any logarithm base, really). The exponential (x^2^) would start slow and then increase fast, and the logarithmic one would start increasing fast and then go into increasing slowly.

https://www.desmos.com/calculator/7l1turktmc