No, it wasn't a percentage. This FI used $900 for the first person and $200 for each dependent. So if it was a couple with 2 kids, the residual income would be $1,500. Don't ask me how they came up with those figures. I presume part of the $900 was for the household itself (gas, electric, etc.) and then $200 per month for each person (e.g., food).
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I hear and I forget. I see and I remember. I do and I understand.--Confucius