The obvious (but not necessarily correct) answer to your problem is that you don't have available relievers. It's one thing to have the Pen set to Aggressive, and another to have available a long or middle reliever when needed. It's sometimes tough to check during an away series since you can't always get the Stats Roster page after each game, but with a bit of work you can reconstruct the BFA's by working backward from the box scores and any Stats Roster pages you were able to intercept. This way you can see if you had the arms and the BFA's to do what you want it to to.

Otherwise there is a bug.

Truth is, my experience with this feature has been that it does seem to work.