It's a woo-woo world out there!
Spirals move energy. Always in the same direction. As demonstrated by tornados. So if our goal is to boost soil the spiral wants to be open to the ground. But if we want to boost the branches of a tree the spiral should open upwards. Yannick has experiments to prove this.
You don't actually need metal at all. I've not run a conclusive test yet but I firmly believe snail shells alone will have a positive effect on the soil. Have also noticed how snails like to die on ley lines. So when I find one, I almost always find a load of them. And into the bag they go ;)