I assume you mean it comes out on whiff, right?
Try the usual input of st.lk xx qcb kk, but press and hold the kk for a moment (avoiding the negative edge).
Often, it’s the negative edge of kk that is released after the st.short whiffs, giving you an ex tatsu.
If that doesn’t work, you might just have to practice and speed up. But holding the kk will make it easier.
This works for any quick empty cancel/buffer/2in1 motion.
You could always replace the EX tatsu with an EX fireball and see if it’s just the speed/direction that you input the motion. It has to be done quite quick.
I’m glad to hear it works for you!
It’s not a problem for me in this game, but I used this trick with gief and his st.short xx ex. greenhand in sf4.
I use my thumb on the short, my middle and ring fingers for the forward and roundhouse.
It’s not. The point of using st.short is that it’s such a quick normal that it’s hard to whiff punish.
You’re not supposed to use st.short xx ex.tatsu in range of their blocking hurtbox.
You’re meant to use it just outside of the range of your opponent’s common pokes. You can throw out st.short xx ex tatsu randomly/predictively at this range to try and pick off the opponent if they walk forward or poke into into the st.short, automatically converting into decent damage and a knockdown for one bar.
It’s useful against Ryu’s cr.forward, Chun’s cr.strong (slide), stuff like that.