i think of slapping as blending with the ground. this is a bit confusing but if you think of uke in the air as stationary and the ground as rushing in , the slap is what matches speeds between uke and the earth.. what I've notices is that when the slap is timed right (and this is not something I can consciously summon, it just happens) it feels like turnign into a charging wall and then rolling off the charge.
this sort of image comes to my mind when I've had a nice fall of sorts. I'm not sure if it's useful but it does help take the fear out of breakfalls for me .