I have tried to explain it. Please note that an important portion of synchronizing reactance is related to armoutor reaction or winding induction voltage (emf). This reaction effect just may be for positive sequence which is synchronous with main rotation field and cannot exist for any asynchronous rotation field such as zero and negative sequence. Also the difference value between transient and stady state condition is related to armoutor reaction or induction voltage produced by stator windings.