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.