Technically, the large cog limit screw is also just a protection device. If the cable tension is set right, it's not even needed. The shifter should never try to go beyond the large cog and into the spokes, unless the cable tension is too high. Shifter design can play a part in whether the screw has much effect. Some shifters may not have quite as positive a stop as others. I've found that I never need the large cog limit screw with Campy 11.