I noticed awhile back that when I lied back at the hair salon while getting my hair washed I started coughing up gunk. I noticed the same thing when reclined at the dentist. That clued me in that I needed to lie back in my recliner to get up the gunk. I can sit upright all day long doing airway clearance techniques and get nothing up, but then lie back and it starts flowing. I guess my message is to spend extra effort just noticing if/when the gunky cough starts and tailor airway clearance accordingly.