I guess that depends on the metric you use. You say they should be punished by time (and so people who earn money more quickly should have to pay more). However, I see many problems with that and I think it would result in much less fair fines than now.
Picture two persons, one living in the countryside, one in a big city. The second person earns considerably more than the first because life in the city is just more expensive. Both persons have the same amount of money left at the end of the month (after paying the bells etc) but income-adjusted fines would mean person B would have to pay way more.
If it’s posession-bases instead (i.e. your fines depend on what you have/own) then what about some person who inherited a large house that is worth lots of money and has an otherwise normal job. This person may also have the same amount of money left at the end of the month as the other two persons but because of his big house, he’d have to pay even more, potentially sell his house because of a small offense.