I am convinced that when it comes to "erotic story telling" you have a lot more experience than I do. Yah, I have experiences of my story "veering" but all for the wrong reasons and all because ... I was a willing newbie who didn't stop to think about what might happen.
And I can really laugh at myself in hindsight.
Before I go on... apologies if I sound overly dramatic but part of the above is courtesy of my gf, who has been in support of my digital erotic fantasies from the moment I fessed up.
SO...
I am a sucker for the "damsel in distress" trope, it can seriously trigger my mood. Even if nothing really happens like in this post (for the random readers: that link shows you 2 topless girls, an evil "sister" behind 'm while they're faced with a dragon).
A lot of my earlier stories (which aren't that many yet) led up to me working towards the highlight. And then the "silly male syndrome" kicked in; according to my gf. For the record: Yes, she poked fun at me, but also with the best of intentions. No politics pls....
See... I can more than often still get. ... "excited" about my own fantasies. But the problem with that is that some of my poses and work quickly lose appeal to me. And that had its effect on my work.
To be fully honest it also didn't exactly help that the one moment I did "push it through" was also the scenery which I ended up disliking the most of my work. Though I suppose the water splashes really did carry their part ;)
So these days I try to work backwards. As my gf likes to say: "Rescue the bitches first, THEN roast 'm because of it", which both made me laugh but also gave me some really good ideas. Because this works seriously well for me!
These days I work out a rough story, if said story has some "sexual fantasy climaxes" I first focus on the "boring" aftermath(s) and then slowly work my way back towards the sex scenes.
And you know what the best part is?
This experience even helped me to improve in other areas as well.
Bottom line: for me, working on erotic fantasies is a lot harder than it seems, especially if you want to make sure to please your audience as well.
I suppose not fully comparable to your setup but IMO still related.
FOR the record... I am >< close to finishing my re-do a render ... for the redo the render fun-contest!