I felt like the Emhyr knew that Geralt was lying, which was interesting because Ciri then asks him if he believed it and Geralt expresses some doubt. It was a scene that deserved a little more depth, because I felt it was essentially the Emhyr accepting the circumstances and willing to let Ciri go. Realistically speaking, even in the epilogue "Ciri's exploits are known". How could this fact not reach the Emhyr? It was his acceptance to let her walk her own path. His frustration of this fact was directed at Geralt, telling him "I never want to see you again". Because he knew it was probably Geralt that influenced her decisions and prevented him, the Emhyr, from getting what he wanted, i.e bringing her to him (this assumes the Witcheress ending). I think he leaves Geralt and Yen alone because he knew that without them, Ciri would still be in danger or dead. This is also interesting because it could be viewed as Geralt himself influencing Ciri's actions, but I did feel that Geralt was trying to channel, at least in several of the chosen prompts, to allow Ciri to be herself. This is why his tutelage and mild 'pressuring scenes' in the epilogue felt out of place. He was willing to let her be herself throughout the entirety of the game (for those that chose it) and in the end he is pushing her to a certain outcome...it felt out of place.
But back to the Emhyr: so even under his calm visage of contempt (and this could probably very well be out of character for him in the books), he was willing to let go, accept the circumstances, and let Ciri do what she wants. After all, my take on the empress ending was that (at least how it seemed to me) Ciri wasn't doing it for herself, she was doing it because she was influenced and/or guilted into making that decision, which wasn't really much of a decision at all. Her sadness and reluctance combined with her acceptance of the situation though without any enthusiasm, demonstrated to me that she was, once again, allowing herself to be used: just as Avallac'h used her to stem the White Frost. Sure, she might have done it on her own volition, though the question is whether or not she would have done it without the coaching, and opinions of her mentor during their sessions.
Ciri, seems, after all, to be a bit impressionable though good-natured and empathetic, and people take advantage of this fact. As for her own wishes and whims, I thought she made that clear in several instances over the course of the game, she wanted to be free, she wanted a playful, interesting, adventurous and 'simple' sort of life away from the grand machinations of world politics or extraterrestrial doomsday scenarios. But due to her empathy and due to her not wanting to see others hurt, people exploit this and 'Grima Wormtongue' their own ideas and ambitions into her.
Of course a bit more exposition on her own thoughts, as well as that of others in what they wanted her to do (Emhyr) would have provided a lot more insight into all of this, but instead we are left to somewhat speculate..maybe that's for the best, maybe not.