i shoot the s nocks and like their performance. i also shoot some aluminum arrows with nirk nocks, and even though the knocks have a lot of area to grip, they do not hold the string as well as my s nocks do. the s nocks are by far my favorite type of nock, mainly cause you buy them just about anywhere and they are priced fairly decently. but as mentioned above, i think string pinch comes from the actual angle of the string caused by extreme angles or too much tab or glove..have you tried switching up between tabs and gloves? it helped me and i realized i needed to go down a size in the glove i was wearing...i stretched the leather a little bit (it was a lil tight around the fingers) and the smaller size fixed the string pinch...maybe there is too much material there including the knock, tab/glove, and your fingers? hope this helps
jesse