I understand immanence as "present as a natural and permanent part of something". That naturally means that something which is immanent cannot be omnipresent (it is immanent within something else where it is not). That would already require two "substances" plus space. If immanence (and implied duality) meant just "the other side of a coin", the whole concept of immanence is moot (or illusory) because we are talking about the coin in its entirety.