This narrow baseplate is made for when a doorbell is in the corner and need to move the swivel away from the corner.
If using with a 90 degree mount, the movement will be limited depeding on the width of the bracket. For instanace it may be able to only adjust 30-90 instead of 15-90. Also if using the 35 degree mount, looking straight out may be limited , but only slighly as you can angle the doorbell away from the wall
The holes are in line with the base of swivel mounts at 2-3/8”. Hole spacing cannot be customized with this mount. It only works with the swivel mount. Only the narrow piece is included.