...
Reseller level
To set in on the system reseller level go to System Administration → Resellers and open the reseller that should be configured. Set the following property to the number of digits that should be masked. Note that this value might already be set in the list, if so click Edit to change the value for the property.
...
Customer level
To set in on the system customer level go to System Administration → Customers and open the customer that should be configured. Go to the Properties tab and add/edit the following property (KEY=VALUE) to the number of digits that should be masked. Go back to the Settings tab and click Save
...
User level
To set in on the system user level go to Administration → Users and open the user that should be configured. Go to the Properties tab and add/edit the following property (KEY=VALUE) to the number of digits that should be masked. Go back to the Settings tab and click Update
...