Cf ranking for Japanese is ordered by discourse grammatical function as follows (Walker, (2) (GRAMMATICAL OR ZERO) TOPIC > EMPATHY > SUBJECT > OBJECT2 > OBJECT > OTHERS (Walker, Iida and Cote, 1994) This ranking explains that the higher element in the Cf is likely to become the Cb ('backward-looking center') in the current utterance.
in English, the subject is the highest candidate of the center, while in Japanese the topic is the highest candidate of the center.