Javi vs. Tuga (aka Twin) Stream!
(First Fox match at 12:30)
It depends on which part of the dair they hit and how far you DI'd the previous shine. If I hit you with the front of my shine and you DI it really far in front of me, I will barely be able to reach you with the dair. So if I am barely tipping you with the dair, SDIing it will make it so the shine is pretty much guaranteed to miss. If you only slightly DI the shine, the Falco might overshoot his dair (anticipating further DI) and if he is really far into your body really high off the ground when you SDI, you can go back into him and as he falls to the ground he won't be close enough to hit with the back of his shine.
It's a lot of little spacing variables that you kind of just have to understand intuitively through practice. Especially when you add in how the Falco is waveshining, there are a lot more things both players have to watch for.
@commonyoshi
Yes, you should stop. A good Falco will destroy you for DIing in at the ledge if you do it every time. If there are platforms, you can pretty easily escape onto them. I am pretty sure that even on DL from 0%, after one dair-shine, the next dair-shine iteration will pop you up high enough to land on the platform. Falco's punish is much weaker off of platforms than it is off of the ground, and the extra shine-waveland he will have to add in makes his shine stale that much faster (meaning he will have to start utilting or doing other stuff to continue the combo).
@17:25 in the stream, there's a perfect example where Javi SDIs Tuga's dair behind him.