Never seen what your describing but I have seen them in the standard s curve defensive position and in the vertical mating dance position where they do get vertical but still have at least 50% of their body laying flat.
http://www.youtube.com/watch?v=uNXe79MKXQk
I have seen snakes raise up their heads and part of their body in the preparation for a strike. I have seen pictures of snakes mating like you posted but that is not what I saw that day. I said I heard it rattle but I also heard the snake hiss very loudly. I wish someone had been with me that day so they could have seen it too. I will continue to look through art books for the old western painting that I described to you.
On another subject we knew an old rancher/farmer in Brazoria County whos real name was Dusty Rhoads.