Master Yuan's divination cannot be completed in one go because after the mutated soul is adjusted, Feng Jun still needs to check the result.
It's really unavoidable; no matter how adept he is at divination, he cannot predict the result of someone else's cultivation of a secret technique. Even when he and Nie Chifeng practiced the Chaos Kanli Secret Technique, they had to constantly monitor their state for timely adjustments.
However, Master Yuan's overall condition is good, his cultivation level is at its peak. Although it has been close to three hundred years since he devoured the Heavenly Demon soul body, he remains highly vigilant because he instinctively recognizes that something is amiss, thus his soul has not been assimilated by the Heavenly Demon soul body.
On the contrary, his cautious nature caused his Consciousness Sea to undergo mutation, which is relatively easier to handle.
