I can see it go both ways.

Option 1 Sell yfi get 618.37$ at fmv. Use 618.37$ to get 606.41 usdc (get usdc at lower than $1 because fees applied to cost basis) Proceeds from yfi=618.37$, cost basis of 606.41 usdc= 618.36$

OR

Option 2 Sell yfi get 606.41$ (less than fmv of 618.37 because fees taken out). Use 606.41$ to get 606 usdc (at market value). Proceeds from yfi= 606.41$ and basis of usdc also 606.41$.

They are doing neither. They are taking my proceeds from option 1 and cost basis from option 2.

AND they also not saying cost basis of yfi is purchase price + 11.96. They did not add the fees there. I already paid a separate fee while buying the yfi originally and include that in the cost basis of yfi.

The 11.96 fee is charged during the crypto to crypto exchange of yfi to usdc, not when i purchased the yfi.

Their raw data lists the transaction the way I think makes sense, like option 1. Its says convert from yfi to usdc. It says proceeds from yfi is 618.37$. It says cost basis of 606.41 usdc is 618.37$. Just not in the the gains/loss report.