I talked with John Navachek (Dayshift Slot Supervison) and he assured me that it was their intention to keep an even mix of Pentagon strikes. He said they were not required to but it was their intention.
I suggested that us collectors were selling back the non Pentagon strikes and they were re-using these as hopper fills but he said that this does not happen, that each new fill comes from the vault. He said he would investigate the vault to make sure they were filling each rach with an even mix of Pentagon strikes. I will know more this weekend when I give the strike machine another play.