This is right, I believe the builders even had capstones that rocked just like the logan stones that inspired them in the first place, George is right and common sense doesn't come into it, it was all about what impressed the most or/and was defying nature the most, eg madly sloping stones or ones that even rocked, those Irish ones [like Aghnacliff Portal Tomb - http://www.themodernantiquarian.com/site/2015/aghnacliff.html] with it's 3 stones on one side supporting the capstone certainly defy logic.