Counter-hit trapping is something that you get from observing people’s habits.
When it comes to beating crouch tech, the Japanese call it “gruppe tsuboshi” (basically “throw tech crushing”). Daigo once claimed that he is the best in the world at beating crouch tech, and one of his personal goals this year was to learn everyone’s teching habits in order to build a successful anti crouch tech strategy against them. That should be enough to convince anyone that with Ryu, counter-hit trapping is based on your opponent’s habits, not hard rules.
For that, you need to observe when they tech (eg. do they prefer a 4f crouch tech, or 3f jabs etc), how they tech (eg. standing, crouching, OS tech with cr.mp etc), and what timing they use (fast, slow) etc.
I find that the best time to go for a counter-hit trap is after getting them to block a jumpin (especially a x-up), because you can control how much frame advantage you have by hitting it high or low. One technique I use is to hit high up for slightly less frame advantage, then following up with st.hp (or cr.hp) xx fireball. I do this because if they tech late, I get a counter-hit. If they do it slightly faster, I get a trade which I OS with Ultra 1:
That won’t work against people who mash stand tech, but in that situation you hit the jump-in deeper, and go for the cr.lk instead. When I’m facing someone that techs really late, I follow up the j.mk with close st.hk instead. On counter-hit (good stun damage) and trade you can combo into sweep.
Neat trick: If you hit a deep j.mk x-up and combo into close st.hk, it becomes a mid-combo meaty and will combo into sweep even though there’s no counter-hit.
In a pressure situation, stuff like cr.lk, cr.mp work well against certain chars because of the nature of their hitboxes. If you can perform the trade OS easily, the cr.lp followed by delayed st.hp is also really good and will make them think twice about teching. Again, st.hk is also good because it combos into sweep on counter-hit (or even on regular hit against crouchers) and it’s very easy to combo off the trade.
Against characters that have slow crouch techs (5f), you can abuse SPS after a safe-jump (only if the opponent utilizes delayed teching). Most of the time you’ll get the counter-hit, and on a trade you can combo into what ever (I usually mash sweep and if I confirm a regular hit, I DP instead).
It’s also important to note the frame advantage after things like blocked level 2 (it’s +4f, so st.hp will score counter-hits against mashers), and things like fireball FADC. I get a lot of mileage from Ryu’s close st.hp. If I have another counter-hit heavy match I’ll post it so you can see the techniques I use.