You could curve the proportion to income to scale impact to something more equitable. How you decide what’s equitable would be another problem to solve, but I imagine it would involve benchmarking around the middle class and poverty line. Right now fine rates are okay for the middle class, so keep the proportion similar, fine rates really fuck up poor people, and fine rates mean nothing to the upper class. So imagine you you feel would be a fair impact for a fine and scale it accordingly.