@TheMaster_Rahl
First of all, I agree with your assumptions.
1.
I am 100% sure that this is not dependent on momentum in any way. If you just jump and airdash and land without whiffing j.A or even just stay in place and dodge Kohaku gets behind them. It is also not dependent on them waking up - you can cross up even after they have woken up provided they do not move.
I do think this is some kind of a glitch, because in both cases (crossup and no crossup) the sprite is in the exact same position. The only other explanation I can think of is that the game uses a measure of distance that is less than one pixel. (This is just an assumption, I do not know how the engine works.)
Also, it seems this is not character specific - it worked on VSion, Nanaya, Kohaku, Nero (didn't try on others). It obviously will not work on Ries because BE4B OTG whiffs on her by default.
2.
I do not believe this is based on BE4B 2C 236B~C timing, because just going for this without the prior combo I can never get the crossup. I also tried doing it from minimum/maximum distance away - same result.
Tell me, is it very rare that you actually cross-up? Or do you get cross-up about as often as non cross-up?
Yes, it is far more likely to end up with the normal non-crossup in this situation. For a time I was almost sure that holding 4 during and after the first feint gives the crossup (strangely the first feint, not the second one that can change the last 2C pushback), and even got it to work 3-4 times in a row... but then some time after it didn't work out. So it was some other kind of delay/timing I had done subconsciously related to this.
Your theory of how pushback works seems legitimate. The only thing that makes me wonder is that there was no visual difference in the position of the sprite of VSion. Even if Koha is in a different position, her spacing shouldn't make a difference if the spacing of VSion stays the same.
I did compare the videos in 60 fps frame-by-frame and yes, there is a difference in delay, however I cannot get it to work consistently... so in the end I still have no idea what causes this.
Regardless, I'd say that if you want to consistently have the option to cross-up in the corner, just leave out the 2C and end with BE4B.
Yes, this is how I usually do the mixup, and it works pretty well. However, this is like completely unreactable under any circumstances and I want to know the mechanics behind how it works. Also, IAD after BE4B gives no option to uncrossup. What I do is jump forward -> 3-way mixup.
Thanks for the input!
@Tonberry
I am 100% positive it is not the IAD timing, although there is a difference in the video example. See arguments in point #1 above.
I'll do more testing when I have the time, and report if I have any findings. If anyone has a theoretical idea, or a practical example, please share.