I think the way Miro rendered the scene is fine as-is. The gravity and motion seem realistic. Furthermore, the couch seems moderately firm and silky, meaning Tara gets to coast a little.
Plus, I am pretty sure the weight of Tara resting on her belly, only serves to increase the tightness of her coochie – which is kinda the whole point. That's probably why Sayako is making that 'orgasm overload' expression!
I slowed the video down to .1x speed and... while I agree with IBT that Tara would 'want' to be oscilating her hips more, I also understand that Sayako is probably greatly enjoying how Tara's belly is sliding back and forth over that cushion; the bulge of her big cock receiving additional stimulation from the weight of Tara's body -- Tara always on the edge of overbalancing; only Sayako's guiding hands on her butt maintaining the perpetual motion. Tara's just desperately trying to hold on; and loving the feeling of being controlled... dominated by her new girlfriend.
IBT quote: "Sayako needs to lick her lips at some point during this. You can keep all of the other motions the same, but toss in a single loop (or two) where Sayako licks her oh-so-kissable pouty lips with her tongue while looking directly into the camera. That then "tells" the viewer that Sayako is REALLY enjoying fucking her cock into Tara's ass again, and by doing it while looking into the camera she's "teasing" US with showing us that she's knows WE'RE watching. Extra bonus points for adding a suggestion of eye animation (subtle flutter?) while she licks her lips in satisfaction."
I don't think Sayako's much of a public tease, meaning her eyelash-fluttering, lip-licking reaction would need to be subtle – more a helpless reaction to the phenomenal sensation of plungering Tara. Truly, Sayako should not be 'showing off' for the viewer; rather she's just so overcome with pleasure, she no longer cares/minds that there's people/cameras watching. ...A subtle difference, but I feel an important one.
IBT quote: "I want Tara's jaw to move and not just hang open in a constant position the entire time. I'm thinking jaw drop/open on the in-strokes, implying that Tara is inhaling (with feeling!) and then rising/closing on the out-strokes as she exhales. You can keep her mouth open the whole time, but just move her jaw a little bit through the loop cycle."
Maybe it would be better to just keep things reversed, as they are in the video. After all, Sayako's dong is SO big, she seems to be working Tara more like a bellows – (Tara exhaling on the in-thrusts _ as Sayako's flesh-pillar literally rearranges her organs, then gasping air back into her lungs on the out-thrusts). With that in mind, imagine if Sayako thrust in and then just... stopped: A naughty move where Tara would tempor-air-illy be unable to inhale; every nerve in her curvaceous rectum desperately signaling an over-poweringly stretched, FULL feeling. Her eyes would roll up in her head, tongue lolling out in text-book ahegao...
But then Sayako would pull back -- Tara's lungs fill with air, the platinum blonde recovering her senses enough to glance back at Sayako with love in her eyes.
IBT quote: "Something else that would be really nice to have, but which would be a lot of work to do, would be to have Sayako "bottom out" inside of Tara and then hold that depth while grinding her hips into Tara's crotch. Then, while she's doing this "deep twirl" motion with her hips, Sayako (possessively?) swirls her hands around on Tara's buttocks, enjoying their resiliency, before putting her hands back into their position at her hips and withdrawing her cock for more in-and-out fucking. Something to break up the "monotony" of just slowly pumping Tara's ass."
I like the abrupt camera movement @ 1:05 that seems to almost catch the attention of Sayako – (who was just previously 'lost in bliss') -- causing her to abruptly remember/acknowledge she's being filmed? Her reluctant willingness to let others watch, seems to be overruled by carnal possessiveness over her new GF.