Proof of this, is what I feel is the worst scene in the game... Ann's motel scene. No logic whatsoever for how that plays out. Especially if you've never shared Ann before.
Hmm i disagree, i thought the arrangement of that one was pretty logical.
If Ann "hates" the MC then she'll invite the guys on her own after MC is asleep, and fuck them.
If Ann and MC are together then if MC chooses to sleep on the bed with her and shares it with one guy, she'll only fuck the guy (s) if MC explicitly suggests it to her. Otherwise she'll stop herself (or fuck MC if you go for this option)
If MC chooses to sleep on the couch and has Ann share the bed with two strangers then both the game and Ann take it as a signal MC wants to see her involved with them, and she does.
Sure, it would be nice if there was some talk between Ann and MC regarding this (there's even good opportunity for it, with Ann already approaching the MC on the couch to talk before they all go to sleep) because otherwise it can appear very abrupt, but even without it there is some clear logic to it all.
The only thing that felt off in all this was what i mentioned before, that it all goes out of the window on the next day if you choose to give the guys a lift. But that seemed more like oversight/bug that didn't take into account Ann's earlier behavior even though it is one of the switch branches.