In the classic stroke, the gentle hold on the cuestick combined with giving the entire shooting arm free rein to move, allows the cue to brush the hand so that the third and fourth finger come mostly off the butt of the stick.
One key to the movement is to allow your cue to move through your shooting hand and for your cue to adjust in the fingers of that hand without conscious effort.
Pool players often learn by imitation, and it is unfortunate when one sees a pro roll the cue through their hand then tries to roll their own cue by conscious effort. Trying to consciously move the fingers, rather than letting the cue shift through the hand as a result of momentum, will toggle the stick off the path it should assume through the shot. This very slight cue movement and hand movement will not occur if the cue is rigidly clenched.
Your rear fingers might lightly grip the cue, brush the cue a bit or come free entirely.
