529 START Married AGI for “Earnings Enhancement” Question

Apologies if this is buried in the FAQ somewhere that I haven’t been able to find, but I’m trying to figure out how, precisely, the AGI for the “earnings enhancement” is calculated and applied. As a starting premise, I understand that there are no joint accounts, and it’s the AGI of the account holder that matters. However, the implication of that, that we can create the account under my wife’s name and get a much higher match than we would if we created the account under my name, when we file married filing jointly, seems more than a bit fricky. Is that actually how it works, or would our total AGI be used regardless of which of us owned the account(s)?