Quote, "For the purpose of these attacks, the monk's base attack bonus is equal to his monk level. For all other purposes, such as qualifying for a feat or prestige class, the monk uses his normal base attack bonus." I'm choosing to see the Power Attack changes as a tiered feat. Thus for the purpose of the feat, your BAB is 12, not 16. Same would go for Combat Expertise.
Regardless, check with your GM. In the end, it's their call.