This isn't how the tax regulations are written. If you have non W-2 income it is automatically presumed by the estimated tax regulations to have been equally earned over the course of the year and hence you're required to pay equal withholding over the 4 quarters. That is the default requirement. You can specifically request a waiver from this if you have a demonstrable event that caused you to earn the money later in the year, and in this case the IRS will specifically look at the circumstance around your income and decide if they can allow you to go against the default and only pay estimated tax later in the year. But remember given the regulations presumption, it is you who must demonstrate when your income occurred and specifically ask the IRS to examine it, and if you can't demonstrate that it occurred later in the year, the default is that it occurred equally over the course of the year. So no digging is required by the IRS, it defaults to equal estimated tax payments and they only dig when you specifically ask them to in order to receive something other than the default. No value judgment on that, it's just the reality.
