A simple solution (probably used in many places) to this problem is to have brackets. Everybody is taxed 6.6% on its income until a certain threshold and the re

A simple solution (probably used in many places) to this problem is to have brackets. Everybody is taxed 6.6% on its income until a certain threshold and the rest is taxed at 50%. You can add more brackets as needed. And so, there is no incentive to be just bellow a certain bracket threshold.