In most cased what every geometric form you are using -- you are creating a space "between the worlds" As the old Pagan Way saying goes it become a 'place that is not a place. in a space that is not a space. in a time that is not a time --- separate and apart"
When i am casting protection, it is a sphere, same as Saulamay. I even do that whenever i go anywhere public (have the sphere around me to protect me from the energy and emotions of others). When i raise energy, for me, it is a toroid (which is probably why that came to my mind when i posted earlier). I pull energy from the earth, through my feet, and it exits the top of my head. It flows back out and down to my feet. And, along with still pulling energy from the earth, it is pulled back in through my feet. It builds up in that way until i direct it with intent (either to put energy in something or to cast it for my working, etc).