There's a new Guile on the scene lately with the nick tsuyoshihyuga who does Guile upside down kick, cr.mp, flash kick. For the life of me, I can't get close to pulling this off. I can do cf.hk, cr.mp, lp sonic boom and cf.hk, s.mp, lp sonic boom fairly regularly. But I can't figure out the timing for what tsuyoshihyuga is able to do so flawlessly.
Here's a video of what I'm talking about, although in this one, he only does it once.
Does anyone have any suggestions or help for how to do this?