IMO, fall damage (the actual amount, not the ratio) should NOT scale with the current max health. Falling from a certain distance (enough to trigger fall damage of course) with no enchants should do the same amount of numerical health damage no matter what your current max health is.
Of course, fall damage should be allowed to surpass your base max health, and if you fall far enough, maybe even surpass your current max health. That way upgrading your health can impact how far you can fall. (This would only be fair if the double digit base health characters are no longer generated, which from what I have heard, their existence is a bug)
However, to prevent abuse, the amount of fall damage you take should be super-linear to the amount of distance you fall (or how hard you fall, or whatever the variable it scales over is). After all, doesn't kinetic energy scale squared to your velocity?
This way, if you double your health, you don't get to be able to double how far you fall, but rather, say 1.2x the distance you can fall. And the returns get even more diminishing as you go on. This should allow boosts in health to increase fall durability without leading to "I can fall from the stratosphere and still live" without using an absolutely insane number of enchants. (Possibly, never reaching that, if the amount of distance you can fall turns out to be asymptotically bounded given the fall damage equation)