FTDK, I frequently travel that track between CS-TL-CS, IFR and VFR. When VFR it's always different. I'll make a CTAF call approaching Dunk from the south, then hear a call from a meat bomber over Mission or Tully.Usually follow that with an Area Freq call. Sometimes ATC will assign a discreet code, sometimes they don't. I am guessing that it is purely based on traffic and "bombing" activities.
Did Bob have a theory?