Any way to know who Piett marks when on defense?

I just started running Tarkin (L), Vader, Thrawn, Palpatine, and Piett in arena. The idea is for Piett to mark Tarkin (I loaded Tarkin up with protection and potency to make him durable, and the assists will theoretically continue to boost his defense) but I don’t know how it would work on defense. Does anyone know enough about how the “AI” treats imperial ambition to make sure that Piett always marks Tarkin?