When the fascia on a gable end of a roof does not wrap the corner, the end is mitered. You can specify the mitering option: vertical, horizontal, or perpendicular.
The mitering options of a fascia can not be changed if the fascia either wraps a corner, or is not on a gable end.
Vertical miter
Horizontal miter
Perpendicular miter
Gable end fascias are mitered to match the rafter cut of the roof.