Can someone help me out with the math here?

You probably forgot that
power db = 10 * (P1/P2)
voltage db = 20 * (V1/V2)

which is way you are off by a factor of 2.

Or to put it simply, if the voltage doubles, then the current also doubles
and since power is volts x current, and 2 x 2 = 4, then the power increase
is 4 x if the voltage increase is 2 x.

Hairy R. Beanz
(On second thoughts, forget that - probably never get away with it !:-)