So your 7% is based on the 107 days your contract ran. If it had ran for a full year, hence an "Annual Percentage Rate" it would be around 25%.
No, the 7% is the annualized rate for the V2, on the next tab for V3 the annualized is 12.73%.
I think the 25% comes from if the same amount of profit was paid as the first block of every contract, for every block. That gets me to around 25% I believe, but that is not really a fair way to evaluate the asset.
As always, you've out-mathed me! ;-) Thanks for the analysis.