Blunt noses are best at subsonic speeds because they provide the best shape for the air to get out of the way. From [this site][1]:

> The speed of "sound" is actually the speed of transmission of a small disturbance through a medium.

[![From an old uni book][2]][2]

The picture shows a single point traveling at a constant speed V, emitting small disturbances :). The air in front of the travelling point is forewarned, and is pushed out of the way isentropically, without losses. It is this part of the subsonic airflow that is key to the optimal shape: a parabolic one.

[![enter image description here][3]][3]

If our travelling disturbance is not an infinitesimally small point but an actual 3D body, its optimal shape is the same: parabolic. Notice that in your figure 20 the first shape is parabolic and actually has a negative $C_D$: it sucks itself into the airflow. None of the other shapes do, not even the hemispherical shape 2. With subsonic incompressible flow, it's what happens in front of the nose that creates lower drag, not at or beyond the nose.

That's all valid when the shape travels at a certain speed, at zero Angle of Attack. 

* At any other speed, the optimal parabolic shape is different, still a parabola though. 
* At any other AoA, it is very difficult to create a parabolic body shape. But a spherical one comes close, as your Figure 20 shows - the first bit of a parabola is close to a sphere anyway. The larger the sphere radius, the closer it is to the optimum. 


  [1]: https://www.grc.nasa.gov/www/k-12/airplane/sound.html
  [2]: https://i.sstatic.net/Y9hIW.png
  [3]: https://i.sstatic.net/DSOPG.png