BIS report: higher taxes on larger banks

A new study by the Bank for International Settlements (BIS/BIZ) suggests that large banks should be taxed at a higher level to compensate for the risk that they pose to the taxpayer. But I think that differentiating tax rates for of different size would open a can of worms - what is the right level of tax? what size is the cut-off point for different tax rates? A more simple way to restrict the trend to ever-larger banks would be to limit the (implicit or explicit) state guarantee to a certain amount. This would give an incentive to clients and depositors to spread their business around and lead to a more balanced industry.