Free Step Dodge

Which move? Kasumi's hitboxes are trash and Phase 4 inherited some of them.

4K. I was trying a 66T setup where I go into 4K P+K chifu K P+K tenfu T

Nothing's iffy. This game is not like VF. When you do a i19 move and the frame advantage is +20.. it still doesn't mean it will work. It takes 5 frames to turn around and your doing an i14 moves. +10 = 15 frames to turn around.

And when your doing an i14 move when the opponent takes 15 frames to turn around.. it's not going to work.

4K is high so opponent can crouch after 10 frames and avoid it.

With Kasumi sometimes when I parry and use 6K (a tracking mid) on someone's back, all they have to do is stand still and they'll avoid the kick. Her entire leg will clip through their body and the game will register it as not hitting.

That's only guaranteed if the opponent is -14 or beyond when parried, Chapstick. It'll work on Phase 4 since she has moves that are -14 & -18 when parried (3P & H+K but I have to go back & look). Nereus is right. You should be using moves around 11i or 12i from 66T on opponent to get a guaranteed.