Firebird isql exclusive mode?

I have a vague recollection that Firebird's isql utility will in some situations make an exclusive connection to the database, meaning that any other connection attempts will be refused. I fail to find information about this. Can anyone explain in which situations this happens, and in particular how I can make sure it does NOT happen? My intended usage is to execute some commands/queries in a scheduled task, and I don't want to run the risk of blocking other database work while this task is executing. From a few simple tests it seems like I get an exclusive connection, i.e. no other connections are allowed, when there are no other connections present. Conversely, if there are other connections when isql connects, isql's connection doesn't block other connections. I tested this with Firebird 3.0.4 in superserver mode and FlameRobin, using the same database alias for both isql and FlameRobin connections. The alias is defined with an absolute local file path. Should I include host and port to ensure that isql always connects through the superserver (allowing other connections) rather than opening the file directly (blocking other connections)?