iSymphony with User Manager Link

Using FreePBX User Management Module version 13.0.69 and iSymphony module 4.1.18. iSymphony is configured for linked user accounts with FreePBX User Management. When selecting enable iSymphony for the user in the user management module, it populates the user in iSymphony correctly. However, there doesn't appear to be any method to give the user access to additional extensions in the iSymphony module. In the iSymphony admin, I can select multiple extensions and it works properly, but of course those settings are overwritten whenever a change is made in FreePBX. The documentation (http://docs.getisymphony.com/display/ISYMDOCS/FreePBX+Module+Administration) references an "Additional Extension" area in the users module, however this field does not appear to exist in my FreePBX installation. Where should I be going to allow iSymphony users access to additional extensions when using the User Sync feature of FreePBX?