Terminal Box with Multiple Connectors

Terminal boxes have 2+ duct connectors. When you use Revit lib families and add a box to existing system it asks you which connector to use, so you can create system from box to air terminal, and another system from box to air handling unit.

But when I use Titus created box it does not ask which connector, simply one connector gets added to system, the other remain as default. Tried linking, unlinking, changing primary, all to no avail. Any idea how to modify manufacturer family to behave like default one?

P.S. How exactly does the three "Flow Configuration" properties differ?