@Chapstick
The hitbox on 6K is exactly where her knee is and does not extend out. Which is why it now whiffs after 236H+P because the hitbox was lowered on it after one of those patches the game received.
When it was lowered it prevents some characters from going completely under it or through her with mids and lows with no crush properties. The downside to that is, some of her juggles are screwed because of it. In 2u you use to be able to put characters in a sit-down stun and extend the stun with 6K beyond point blank range.
That video is showing the issues with 6K that have always been there since DOA4. In 2U and 3 the kick was fine. The hitbox that it use to have is now reduced to just her knee. So when you play against a character and their hurtbox shifts when they guard, stand neutral and it's evasive, or a situation where a space is calculated and dictated by the game. Kasumi will do just what she did in that video every time with 6K.
Try to slow down with your inputs so you don't get 6K after a parry. You can be counter poked if it whiffs.