Hm, I think Micropayments would only work for regular PayPal account-based payments (aka PayPal Express Checkout for PayPal Pro merchants), not for direct card-based payments.
I'll bring this to the attention of Development staff and see they can do something to ensure that order totals under $12 are directed to the Micropayments PayPal email only if the buyer selects a PayPal checkout but not if they choose to pay with a card.