I personally like jumping down mountains for fun, but looks like he just changed the fJumpFallHeightMin and fJumpFallHeightExponent settings. Open up TESSnip and just change those numbers to what you want - higher exponent increases damage, and higher height decreases damage.
As the name says the exponent setting will exponentially increase damage, so be careful with it.
For anyone who can't be bothered to download TESSnip I've uploaded my personal esp http://www.mediafire.com/file/lida7r26succktb/MoreFallDamage.esp. It's harder than the one the OP was asking for, falling from low heights will cause more damage (and you will already be (slightly) damaged when falling from a relatively low height - in my esp it's 300 units, in vanilla the minimum is 600 units), falling from high heights will cause the same or even less damage - so the heavy armor perk is actually useful. A bit at least. I also slightly upped the NPC damage, but they still need to fall from a relatively high position to be damaged at all. AI is stupid and needs this I think.
The vanilla settings are ridiculous btw. Another example for Bethesda's 'don't make the player feel uncomfortable' philosophy. Even a level 1 character survives a fall 10x his own height. Try to jump down from a spot 60 feet above you and tell me how you feel afterwards.
This should stop me taking so many shortcuts down sheer mountain faces.
Is it possible to do something similar for horses?
I don't know which setting controls horses if you ride them. Either the one for the player or the one for NPCs. You'll have to try.
What I would really like to do would be a mod that makes you slide down surfaces that have an angle of more than 60° (and take damage if you slide too far, just like falling). It's pretty stupid that you are Geckoborn and Dragonborn at the same time. The same concept is implemented in a lot of other games, I just don't know whether it's possible in Skyrim.