I've been having trouble with F-Miyako's BnB. I've figured out most of the problems (623BB timing, 236B immediately after -- sometimes I don't even do it ), but the biggest one was the part after j.421B. I was doing JC into whatever. I got land > 5AA maybe once, then after that freestyled a couple of air combo enders after late JC>j.B into whatever. But I see the general consensus now is whiff air throw after j.421B? I'm guessing this eliminates the need to time the JC and puts Miyako at the perfect height to continue.
Time to go practice! Thanks for the info guys!
There's quite a lot of stuff you can do after the J421B.
One of them is whiff throw, land, 5B > 236A and continue the combo, it's safe and easy to do. Sometimes (and mostly against weird hitbox characters, like Nanaya) you'll have to walk just a bit back to make the 5B land.
You can jump cancel and time an aerial, do something and finish the combo. So far the best I did was JB > 5B > 236A (there's probably something better, though), iirc JC > 5B > 236A does less damage in the end (probably due to a lower correction value). JB > 5B > 236A does more damage than the whiff and 5B (about 100 in Wara), however, against some characters (like Wara himself) the combo will take you and your opponent off the corner and there's nothing you can do about it, so the plus damage may not be worth it.
The most damaging I know so far is whiff throw > 2C > 623B timed B > 236A and finish the combo. It's kinda hard to pull off though...last a-cho videos showed Kou trying to do whiff throw and do 623B timed B right after (skipping the 2C). The bad thing about it is that against some characters (or depending on your timing, I'm not really sure), Miyako will stay behind them (in the corner), so the motion counts as an 241B instead and you'll drop the combo (maybe you can even get punished for it!)
I guess you should try whiff throw always, just because it's safer and easier, also guarantying you the corner against the opponent. Try doing the 5B also because it's safer, later on you can start trying the 623B I guess.