Tboooe,
Yes, they sit under the component and not attached in anyway. You are correct on the positioning of the three SoundPosts as well. They actually come with a tool and a thread which assist you in mapping out the actual center/circumference of each component. It is really quite intelligent as the initial setup is very detailed.
There are several different sizes and choices of wood too for different applications. As, I mentioned I was quite skeptical in the beginning but now use them under every one of my components in my two channel set up. I have tried several vibration tweeks (Sorbothane, Vibrapods, Ceramic Cones, Black Diamond Racing, Myrtle blocks, etc) and the Monument Reference stuff is in a league of its own.
My system is in the virtual systems if you want to check it out..
Cheers,
Chris