It's sloppily written FDIC guidance, not a regulation crafted by the Fed.
When they talk about not charging a fee for de minimus amount, they are suggesting that banks should not charge any fee for an overdraft of less than $XX. When they are talking about the fee bearing a relationship to the amount of the overdraft they are attempting to reiterate the same point; i.e. a $10 overdraft should not generate a $29 fee.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.