It's fascinating to watch how consistently that genre uses the physical setup to dissect control and submission, right? The act itself creates a scenario where one partner is literally on top, dictating the rhythm and depth, which writers can amplify or subvert so effectively.
I just re-read 'A Touch of Silk' by K. Sterling, and the initial scenes play with this so well. The protagonist uses her position to tease, to deny, to control the pace, turning what could be a simple power fantasy into a prolonged negotiation of trust. He's physically stronger, but she holds all the leverage in that moment, and the tension comes from wondering when and how that balance might flip.
Then you get darker stories where the rider isn't there by choice, or where the position is used to enforce a kind of helpless observation. The power isn't in the motion; it's in the forced intimacy, the inability to look away. It strips the act down to pure psychological theater, where the body is just the stage.
I tend to skip the ones where it's purely about athletic domination without that emotional undercurrent. The mechanics are less interesting than the silent conversation happening between the characters.