Assume each vault self-liquidated with a flash loan, plus 13% liquidation fee and auction profit of 3%.
Then all we need to know is the price of Dai.
Dai was expensive at the time, and would have been more so if all vault sourced Dai to self-liquidate (price was already spiking over $1.10 without it).
Let’s say everyone pays $1.20 for Dai.
Vault with 100 DAI debt, holding 1 ETH. ETH price gets to $150, self-liquidate (100 DAI + 13 DAI penalty)*1.03, so owes 116.39 DAI which cost $1.20 each, so $139.668.
Vault gets $10.332 worth of ETH (06888 ETH).
$10.332 back from ETH when it hit $150, so it’s 6.888%.
This is likely higher than in an auction because the price of ETH may have continued falling below $150 during the auction.
The problem is narrowed down to: What would the price of Dai have been?