71,
Maybe a different way of saying it would be....
An 8" tower speaker will play equally as loud as a 6.5" with one/half the amplifier power. Or, you could say that when comparing the 6.5" to the 8", the 6.5" will require twice the amplifier power to equal the 8" output.
Regardless of the power, there is nothing you can do to make a 6.5" have the same midbass extension as an 8" in a slightly larger pod.