These old KS posts had a common problem. If your line got kinked, the lever would have a hard time returning back to the upright position. This taller button makes the red lever start at a higher point, which means that if you want, you can fit a small coil spring around the exposed cable to increase the return force of the red lever. If you try to do this without the taller button, the coils of the spring bind before the post is engaged.

Here you can see how having the red button sit up higher allows for the extra space for a coil to fit.