There is no model form on this. In many cases when a disclosure is required, such as Reg. Z requiring a rate, "prime + 3%" doesn't qualify. In this case, because a range is required, I like the 10% method. But I don't know if making the consumer do the math would qualify. Personally, I would run this by my regulator (and the FRB who "owns" Reg E if they're not your regulator).
My opinions are not necessarily my employers.
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell