That's part of character data. There's just a list of stats that says "likes_cowgirl", "likes_oral", etc.
The game doesn't seem to differentiate between a female giving a blowjob and a male eating a woman out. Both are just "oral" and all that matters is the "likes_oral" stat in the character data.
Right, I saw those stats. Those can be edited in the character files, or just within the game. No trouble there.
What I was looking for the core mechanics of the sex scenes themselves though. For example, the 'lick pussy' action increases the arousal of the one doing the licking rather than the one being licked. That seems like a mistake, because the various 'blowjob' actions have the opposite effect.
And while it's true that the percentages in the character data are part of this equation, it seems as they're modifying some 'core value' stored somewhere. If 'Oral Sex' for both participants is set to 100%, then one partner gets 4.35 arousal per tick (for example, I don't remember the exact value now) and the other gets .9 arousal per tick. For a blowjob, the high arousal gain is on the one getting the blowjob. For licking pussy, it's...the one doing the licking. It's quite odd. Similarly, there's a few different varieties of 69, but some of them arouse both people equally and others only arouse one.
I think it's true that some sex acts are interacted with by more than one tag too. You can have 'Rough Missionary' for example, which is modified by both the 'Rough' stat and the 'Missionary' stat (and the 'Vaginal' stat and the global 'how easily you orgasm stat, except for the Player's character, for whom the global orgasm sensitivity stat appears not to have any effect at all).
So the interactions get...messy. But underneath it all there does seem to be a game system that gives different acts different base values that are then modified in a formula determined by these preferences. I am assuming that same system also assigns which participant gets which base value, when those values are different per participant, but as with the hypothetical 'relationship web' storage, it seems not to be in an easily modified format.
Which is too bad.