Okay, Carissa's subtle nonverbals are reading at the same low level for any pattern he tries, including a set of tactics such that you'd expect at least one set member to have a noticeable effect on most women.
Which suggests that either (Hypothesis 1) Keltham isn't able to read Carissa correctly, at all; or alternatively (Hypothesis 2) that he just isn't using her correct sexual entry codes at all, and she's got Permanent Cheerfulness going on.
Subhypotheses of 1: Does dath ilani training do something that makes women more readable? Does his own training assume the woman is a dath ilani who's had whatever goes into baseline female sexuality optimization?
Subhypotheses of 2: Maybe Carissa has been messed up by this world somehow, untrained and unlearned to operate optimally in the cuddleroom; such that it would take a lot more work to raise her arousal to anywhere near an orgasmic level. Even when Keltham and his agemates were reinventing sex without spoilers, the cuddlerooms had vibrators and lubricants and ergonomic furniture lying around to figure out. Can most women not trained to optimize their sexual responses figure out how to have orgasms, if not supplied with lubricants, vibrators, and ergonomic cuddling furniture?
How sex works in a complete state of nature is not a topic that comes up often in Civilization! Not being in a state of nature is what being civilized is!
Keltham doesn't want to think about this right now! He wants to preserve the heady momentum of discovering sadism, not figure out further experiments to distinguish these multiple hypotheses and subhypotheses!
Carissa is at the very least not acting distressed, and may not even realize that there is any reachable level of sexual enjoyment beyond what she's experiencing now. He can go further into exploring his own sadism and enjoyment, and later go back to giving her pleasure in return.