The Revolution Of The Demon God: Emperor's journey
As their cultivation increased, these similarities would also increase until the 10th stage, where this Martial soul would look exactly like the cultivator with no difference between them.
Tsa Xang's Martial soul was just like this. Although it looked mostly similar to him, there were still a few minor differences that could be noticed, signifying that he wasn't a peak Spirit Establishment Realm cultivator, which was true, as he was still only at the 8th stage of Spirit Establishment Realm.
Tsa Xang cultivated for over half an hour, absorbing the Qi to nurture his soul, and the similarities between him and his Martial soul started increasing, albeit at a very slow speed.