This is the weird part to me. I don't think the marginal payoff is higher for a billionaire, other than in ego or ideological or other less-rational terms.
Someone making 50K who scams an extra 2K out of their taxes has gotten themselves a pretty big boost to their disposable income. While a billionaire already has millions to play with...
I would support higher and harsher penalties for larger absolute amounts of tax fraud, though, because you're depriving your fellow citizens of more if you're keeping larger $$ amounts.