Lowcountry Low Roller
To me, the size of the creature should determine the dice size. So:Falling damage doesn't make sense, overall. Force from falling would not be linear at d6 per 10'. Also, smaller and larger creatures should take different amounts of damage for falling, generally. Force = mass * Acceleration, and the acceleration due to gravity is exponential. Accurate rules for falling damage would be cumbersome. The easiest thing to do would be to have sizes and distance and rolls to make to determine damage, but even then it would be awkward to look up and subject to arguments like crazy. In the end, you'd end up with the dragon killing move to be knocking them prone in the sky and letting the fall kill them... kind of non-heroic.
Tiny: no damage
Gargantuan d12 (or d20 depending on the type of creature perhaps)
That would at least partially account for momentum.