I’ve decided to make the players determine how the thresholds work for Scions. As each Scion can be unique there can be different affect for different characters. If I can get the Scion characters to come to a common decision that would be great. Not expected, but it would be great. I see three basic levels of affect. 1) no affect at all and no potential of extra Fate Points. 2) Suffer suppression inside the threshold and a potential of a few FP. 3) The threshold acts to block as if the scion is a pure supernatural creature, such as a vampire or demon, providing even greater potential of Fate Points.
Finally, if any player ends up with a Changeling, then they get to decide how it works for all changelings in my game.