Okay, so Fe-Anar is now speaking to Keltham exclusively in well-formed Baseline, has mastered all the phonemes, only needs to be told any word once, and can be told whole translated sentences and infer back the words. This is probably impressive and not just because Baseline was designed to be easier to learn than Taldane?
However if Fe-Anar wants to pass as a native Baseline speaker to Keltham, he's going to need to learn some mental distinctions that influence voice tones, now that Keltham thinks about it. Some aspects of pitch in Baseline aren't controlled by language design, they're allegedly free emotional expressions that have nonetheless settled into informal troughs.
The way that Fe-Anar is doing the rest of this perfectly makes it stand out that Fe-Anar, for example, sometimes sounds like he's instructing reality what to do as if it were a person, pronouncing a conjecture like it's a flat statement of fact, or saying an ought-statement at a pitch that makes it sound like an is-statement. You can do that to make metaphorical points, but Fe-Anar seems to not be doing it on purpose?
Keltham apologizes for not being able to state explicit generative rules here. He can just tell that some inflections sound wrong, state why they sound wrong, and say the sentence over again the way a dath ilani would.