To calculate the total contact count , we add up the unique contacts in sync PER connection. If the contact is present in two connections, we count that contact twice as these are two separate syncs we perform (we scan every 2-3 minutes) to keep that contact in sync continuously between the two particular apps in each connection.
Below you find an example: this user has the same Bexio synced to 4 different apps. Some contacts might be syncing in all 4 connections. In that case, we count those contacts in each individual connection. To get the total contact count of 7174 (= Pro Subscription), we added up the contact count of each connection.