I used the Avianca chat on their website and got the following answer.
For multi city bookings:
In this case we will be able to tell what would be the restrictions of the ticket (penalty fee plus fare difference that applies) once the ticket has been issued. Since this will be a combination of fares even if you book them all on flexi.
For "normal" flghts here:
http://us.avianca.com/en/travel-info.../fare-options/ --> and then you have to choose the location of your flight.