I don't know what percent of all audits are done on millionaires. I only know that 1% of millionaires are audited.
If you want to do that math, it's probably pretty easy to do. Have at it. What you're going to find is that the VAST majority of IRS audits are done and lower and middle income familes.
The narrative that we need the IRS to have massive funding so that we can tax the rich is false.