Birds can be frightened or intimidated by their own reflection, so I did not place any mirrors on the front entrance of the birdhouse. The mirror on the bottom of the front side is angled downward for this reason as well.
The mirrors are attached with rubber cement and hot melt glue, and I sanded the mirror edges smooth so they will not cause harm to birds. Time will tell if the bluebirds will actually use it or not. Hopefully I can catch some of them on video real soon!