Is CPF interest computed on a minimum monthly balance?

Here's a copy-n-paste (quote) from the CPF FAQ

(https://www.cpf.gov.sg/member/faq/growing-your-...)

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How is my CPF interest computed and credited into my accounts?

CPF interest is computed monthly. It is credited to your respective accounts by the following year and compounded annually. CPF balances used for interest computation are affected by the transactions in your account. For instance, contributions (including refunds) received this month start earning interest next month. Withdrawals/deductions in this month will not earn interest from this month onwards. There are strict procedures in place to ensure the accuracy of members’ CPF accounts and transactions (including interest payments). To further ensure that our system is sound and robust, our statutory auditor performs regular reviews of formulas and computations in our systems for accuracy, and conducts independent verifications of the transactions and account balances.

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The way the above reads to me is that interest is calculated based on minimum monthly balance (MMB). Correct?

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If that's true, then to beat the 2.5% OA rate with a T-Bill you would basically need 3.33%+ (which is 8/6 x 2.5%, worst case) because the month it comes out you don't get any 2.5% interest on it for the whole month, and the month it comes back you also don't get any of the 2.5% interest for that month too. In addition, there seems to be a $2 bank charge on the transaction in CPFIS OA PLUS some kind of on-going $2 quarterly bank charge, for a total of $6+GST for the 6-m duration. Meaning that you'd need some decent amount invested to make the fees worthwile. I really don't get those fees because they are waived in SRS (as far as I can tell).