Just think of it this way. In our building one bid sheet goes up for every combo job. Everyone from combo to part-time can sign it. If a combo person signs the list he or she gets priority over all part-timers regardless of their seniority. If two or more combo workers sign it the combo worker with the most combo seniority will get the job. If no combo workers sign it or those that did turn the job down the highest senority part-timer gets the opportunity to take the job.
The same goes for fulltime inside jobs. For example we have fulltime feeder wash jobs in our building where someone will wash feeder trucks for a full eight hours. All employees who are considered "fulltime inside" get priority first, then combo workers, then part-timers. The only time I see it act differently is when there are open feeder jobs. They post a list for package car drivers first, then they post a list for only fulltimers and combo workers to sign. Then once in a blue moon they post a list for part-timers to sign if they don't get enough people from the first two lists.
Let me know if this clears anything up!