I am not familiar with this function, but it seems unlikely that the PTE between two scouts would depend on the values estimated for another pair of scout.
Whether you compute the PTE for scouts A/B or for scouts A/B/C, you should obtain the same interaction A/B.
@MartinC Is this correct?
@duanjipeng Please be more specific. How did you get to observe that the values are "slightly different"? If this is something you can reproduce, could you please describe precisely how we can reproduce your observations? (If possible based on the TutorialIntroduction protocol, so that you don't have to send us any data)