Mystics rather like the term Godhead.
"Godhead (or godhood) refers to the essence or substance (ousia) of the Christian God, especially as existing in three persons — God the Father, Son, and Holy Spirit."
https://en.wikipedia.org/wiki/Godhead_in_Christianity
The above definition may relate to mystical experiences. Note however the essence of God indicates that there is an outer form of God that may be transcended by the mystic.
Thus the mystics may operate within their own spiritual beliefs without bothering the theologians of their traditional religion.