This is kind of a visual graphic of what happens with this crazy quake sighting system. It is not a "true" sight which would fire the weapon/grapple in question almost exactly "from" the crosshairs. For instance, if you had the crosshairs of a real rifle over a wall, the barrel would be too, and you would fire over the wall through the sights. As im sure you have noticed with the railgun, even if your sights are over an edge and you are standing straight up and close to the wall, you will shoot the wall, cause the gun fires from chest level and "meets" the sights at infinity. This is the same for the grapple and all the weaps in quake. But, as your model approaches the max look up or down positions, the sight become 100% accurate. (if you are looking all the way up or down over an edge, your sights are dead on.)

As you can see by the picture, the grapple is "shot" from the chest area and it rises to the crosshairs at infinity. In otherwords, if you try to shoot the grapple over an object, the closer you are the higher you must aim. The start of the grapple would scribe an elipse about the front of the model (see below).

But, that's not all! As the model approaches its maximum up and down positions, the grapple alters its "shot" location. When in the max up or down position, the grapple shoots directly from dead center of the crosshairs. Please keep in mind that this is for center handedness. With left and right handedness, there is also a shift in that direction. This also applies to all weapons.