Hitomi midscreen oki is almost non existent outside of specific scenarios. Midscreen your main source of oki is going to come from a 2H+K knockdown on critical stun.
Or you can do things like using 3K twice in a row then running up to 2H+K. I personally dislike this and would rather run Hitomi's mixup or take juggle damage.
At the wall is where Hitomi's oki becomes deadly. She can do P (whiff) > 2P > into any ground hit for a force tech. Most players though will tech on P(whiff) or after getting hit by 2P both of which leave you at alot of advantage.
When you get midscreen knockdowns off anything 1K is the best harassment tool. Earlier I mentioned 2H+K being the main source of oki and that was because if the opponent doesn't tech roll immediately after taking this move they eat 1K.
1K won't force them up however. What it does do is force them to make a decision when they get hit by it. If they do not tech and you do another 1K it's a force tech.