Baba Basra 65a - Halacha like R' Nachman

The gemara tells us (kesubos 13a and Baba Metziah 110a) that the halacha follows R' Nachman b'dinei - meaning that we rule like r' nachman on monetary issues. Our gemara seems to elaborate somewhat on exactly why that is the case. But first we have to know which R' Nachman we are even speaking about. Rashi in Gittin 31b holds that R' Nachman Bar Yitzchok (talmid of Rava) is the stam r' nachman in shas who is the son in law of the Nasi (as the gemara implies in chulin 124a that stam r' nachman was the chasna d'bei ne'siah). However, Tosafos disagrees and hold that the stam r' nachman in shas who was the son in law of the nasi was an earlier R' nachman, who was R' nachman bar yacov, a talmid of Shmuel and friend of R' Sheishes. So, rashi and tosafos argue whether the halacha is like r' nachman refers to R' nachman bar yitzchok or R' nachman bar yacov, but either way he was the son in law of the Nasi.

Now, our gemara explains why the halacha is like R' nachman. R' Nachman asked R' Huna whether the halacha is like r' huna (who holds that a seller sells b'ayin ra'ah), or like himself (rav nachman). R' huna told r' nachman that the halacha is like the opinion of R' nachman - why?

דמקרביתו לבבא דריש גלותא דשכיחי דייני - Rashbam explains that since he was a son in law of the Nasi he was privelleged to always be around the reish galusa who had power that was accepted by the secular government, so he was present when many monetary halachos were being decided. Does this mean he understood halachos of Choshen Mishpat better than his collegues? Not necessarily. Tosafos in chulin 18b and sanhedrin 5a writes that although the chachamim in E.Y. are wiser than those in bavel, the authority on money matters was with the reish galusa in bavel. As Tosafos in sanhedrin puts it the Rosh Goleh in bavel was from "zecharim" and the Nassi in EY was from nekaivos. B'kitzur the reish galusa wasn't necessarily the greatest scholar of all, just that he had the most power. Why would this make the halacha conform with R' nachman?

The gemara at the end of baba metzia says that they asked "shibur malka" who rashi identifies as the king of persia, and the gemara in baba basra 10 says was a goy about a choshen mishpat question and he "paskened" like R' Shimon. Why would his opinion count?

Perhaps R' Nachman wasn't greater than others in knowing every s'mah and shach in choshen mishpat. But, he had the most exposure to monetary issues and therefore had a better understanding of the mindset that people had when making monetary transactions. Perhaps this is what the gemara means when we say that the halacha was like R' Nachman because he hung around the reish galusa. This would also be why shibur malka was consulted. His halachic opinion would not be worth much, but his understanding of people and their intent was more astute.