Information around messenging settings can be found in the article below.

• Preferred Contacts Selection Sequence - This setting controls how many contacts in order should be considered as eligible contacts for notifications. E.g. if set to '3', then it would tell Sentral that the first 3 contacts are eligible for selection.
• Automatically Selected Preferred Contacts Sequence - This setting controls how many contacts in order Sentral would automatically suggest and select to send notifications to. E.g. if set to '2', then Sentral will pick the first two eligible contacts to be the communication contacts.