It depends on the Range of the spell. Spirit Guardians has a range of self which means it surrounds you (the caster) regardless of what space it is cast from. Just like if you cast mind blank or mage armor from another creature's space. It affects you. I never thought of this before but this would complicate counterspell if the creature who's space you were using is outside of counterspell range.
If it is an enamation with a Range in feet, the distance is measured from the "creature's space" and cover is considered from that creature's space.
