There are still times when you all out mash in ver b, mostly moves like Len ex ice/Nanaya chun-li attack, ect. Any move that hits a rediculous amount of times. Other than that though, how the system works, is you hit the button like a moment after the damage comes, so basically you have to mirror your opponents combo. The easiest way to get a feel for it is taking the audio ques from the hits and tapping along with them, like for the generic aircombo damage reduction it's just taptap, tap, taptap, tap, tap(different depending on where the damage is inflicted in the throw from character to character).
If you hit the button to soon, you fail, and I'm not sure on this, but I think you need to leave a little window before you start reducing again. I think that's how it is because if you jump the gun on Len's ex ice/ect and you mash all the way through, you fail the entire thing. And then of course, theres the whole invalid combos bs. Rawr.