The optimal distance between electrodes is the length of the buried electrode. That is, if you are using 8' ground rods, they should be buried 8' apart. You can think of a ground rod as being surrounded by shells of earth, the more earth around the ground rod - the less resistance seen. When you have two ground rods, you want to keep these shells from overlapping and research has shown that the effective area of the shell is proportional to the length of the ground rod. As to why the code book allows us to go as close as 6', I don't know. BTW, I have never seen anything that would allow us to bend a ground rod. It seems that that would create a high resistance spot on the electode.
Laura J
