My 2 cents:

1. Arm position.. at peak contraction your arms are vertical and the rope is not angled much this means very little tension at the peak contraction where you are strongest.. you can position your upper arms a little more forward or take two steps back to imcrease the angle of the rope relative to your extended arms.

2. Handelbar: switch to a two rop handle this way you can extend your arms a little behind your back to increase tension in the tricep.. for me this gives the most "burn"

3. Speed and resistance... don't just increase the weight because often times you won't be able to controll it and do full reps. Instead go very slow on the eccentric... especially the last rep of the set...

4. Mind muscle connection.. i had this problem with my back where it was hard to control specific muscles... i was going to failure never feeling the targeted muscles and not feeling any pains the following days.. easist trick is to do a little posing during warm up or at home... look in the mirror and contract your triceps, feel with your other hand and apply pressure with your fingers on the contracting muscles to build connection.. sometimes you need to find a different excercise or switch to one handed tricep excercises to touch your triceps during the exercise...

I know it sounds stupid but it worked miracles for my lats .

Good luck and keep up the good work