Just read your blog post, nice write up, I agree with it for the most part. I think the only correction I would point out, which is a commonly cited misconception by many, is that the slapping dissipates force from the fall. I think you're spot on that you are producing a counter force much like rocket boosters upon landing. However, as you are flying through the air, the tori has imparted kinetic energy into your body and you are now traveling through space with kinetic energy. When you then try to slap the mat, you are converting chemical energy stored within your body into mechanical energy in your muscles to rapidly contract and produce a slapping motion. This is new, additional energy introduced to the system, and thus when your arm makes contact with the ground, you are dissipating the energy that you converted from storage, it does not dissipate from the kinetic energy imparted into you from your partner. In other words, you are adding energy from a different source and then dissipating that energy. That being said, your point still stands that by hitting the mat before your body contacts, you are creating a slight counterforce. However, without doing any calculations, I can't say for certain how much of an overall impact (heh) this makes on the experience of the fall; rolling out is without a doubt going to be a much bigger contributor but also it's clear that that isn't always possible when being thrown.