The use of "threshold" in Aegis Demon Shield has caused a great deal of trouble. I propose the following rewrite:
[-2] Aegis Daemon Shield - Your very presence, backed by the force of your rock solid Faith, is anathema to Supernatural beings of malicious or ill intent. Effects; The Emperor Protects. You may spend a Fate Point to create a shield of True Faith around yourself and your zone. This shield functions as a zone border with a value equal to the user's Conviction against all supernatural creatures that oppose the user, reduces the power and control of evocations that target characters inside of it by the user's Conviction, and reduces all stress inflicted by the natural attacks of supernatural creatures that oppose the user to characters inside of it by the user's Conviction. This effect only lasts one exchange, but it can be extended indefinitely at the cost of a supplemental action each exchange.
Formatting's ugly, but I think it gets the point across. Ask if you need clarification, complain if you don't like.