I’m not entirely sure how exactly the flux measures this, but I know with the Kickr, it just reports whatever power TR is telling it to produce. So if it is 250 watts, it will hold that resistance with some sway up and down as normal, but when it reports the power to the head unit/phone/laptop/tablet, it will just report a flat amount equal to what TR is telling it to hold. In other words, what it reports is already smoothed out.
Most trainers have a switch on the software side that can remove ERG smoothing. This would be on the trainer side, rather than TR. Here’s a comment from TR about this specific thing for more info: