I'm assuming you also use a bronchodilator at the beginning of your treatments. Tobi can be irritating and swells airways, so if you try to cough up stuff after Tobi it's going to be hard. Maybe check with your doctor to see if you are doing your meds in the best order when it comes to coughing up stuff.
What I do if it's hard to get stuff up...
After hypertonic saline, I use the Flutter -- I'll keep doing it until it works.
But if still congested, I do postural drainage (lying over sofa arm onto the seat)
If I'm sick and need further clearance, I take a hot steamy shower (shower must have chlorine filter on it) or lean over a pot of boiling water with a towel over my head (making a tent) and breathe in the mist. The doctor said I could put some natural eucalyptus in it as long as it's not irritating to me.
Drink hot tea with honey. Especially fresh ginger tea.
And once in a blue moon, when my lungs are really inflamed and congested, I've been given a cortisone shot, to open up the airways. And boy, does that do it.
And as Diane said, exercise does it for me too (but not if I'm sick).