When performing paper cutter chokes, it is paramount to solify the paper cutter grip after it has been secured. One of the most common mistakes I observe when teaching this move is that people settle on whatever grip they initially get, failing to re-adjust it to make the position more oppressive for their opponent.
Once the grip is secured, tori can solidify the grip by using the hand that isn’t controlling the back of uke’s collar to pull on the lapel. Easing up on the grip slightly, the slack can be pulled out of uke’s lapel and the grip re-applied. This significantly tightens up the grip and sets tori up for success to finish the choke or transition to other positions.
Also, it is important for tori to engage their elbow to clamp down on uke’s arm instead of simply relying on pulling with the behind the collar grip. This pins and immobilizes uke’s near side shoulder, making it much harder for them to move and create space.