Бист может быть забонжен эСоршей, так как у него к ней Affinity.
"Описание Affinity."Affinities are special abilities conveyed to some character warjacks when the warjack is part of a specific warcaster’s battlegroup. The warjack gains the affinity when controlled by any version of the warcaster listed in the name of the ability. A character warjack with an affinity can be bonded to that warcaster (see Appendix B: Warjack Bonding, p. 246). The “warcaster” referenced in the text of an affinity always refers to the warjack’s controller.
И, к слову, свой бонус от Affinity Бист получает как от эСорши, так и от пСорши.