It's a rebound only adjustment, so focus on chassis motion on rebound. Basically I mean don't pay attention to how the car feels or moves during the bump. Pay attention to how it moves after the bump. Impact force is compression dependent which is fixed on the Konis. Rebound will control bounding after as well as the sum total motion/oscillations after bumps.
I have not used the Koni inserts personally. I've owned the AGX and the D-Spec.
From my experience, I will suggest that you tweak the front first. Set the rear overly stiff. I say this because the back end bouncing around can affect what you're trying to do. With the back firm, start toying with the front. Go softer, work your way up. You can be coarse at first. Work higher and higher until you start to feel the car fall after bumps. If the rebound is too high, the suspension will have trouble extending quickly after compressing. The car will quite literally fall after every bump. It will feel like you're getting air time. This is rebound set too high. It can also negatively affect traction over bumpy sections and make the car quite skittish. You want to go excess so you can feel and understand what excess is.
Dial it back down. Keep going down. What you'll notice is that air time disappears. Now the tire remains in contact with the road much better. Dial it down more. Now you'll start to notice the chassis bounds and wallows a little more, has a little extra motion after bumps. Go lower. You'll start to notice that the chassis begins to oscillate continuously, albeit slightly. If you look across the hood to the road, you can see the hood bounce up and down and the frequency of the suspension and never stop. The car goes over bumps and there are gross movements, but this tiny bounce is just always there. That is when you're too under damped to control the chassis. Konis do have moderate low speed damping, so there may be less of this than what I've personally seen with the AGX and D-Spec struts. Still, soft will have a lot of chassis movement after bumps. It will bound and wallow.
The ideal point is somewhere in between. You want it firm enough to get rid of the extra motion, but you want it soft enough not to cause traction issues with the tire losing contact with the road. That range may be small, maybe a turn, maybe half a turn. You need to toy with the strut till you find that sweet spot. If you question your ability to do so, repeat by going excessively stiff and then excessively soft. Go up and down the range several times. Get a feel for it. Train your mind to recognize the variation in chassis motion. Then tweak again and find that sweet spot.
Why'd I say the front first? Well, the back end is hard to feel from the drivers seat. You get a good sense of the front end from sight and feel since you're sitting on that end of the car. You have a significantly harder time feeling out the rear end. I say set the rear end stiff just so it's not bouncing around and affecting what you think you feel on the front end.
Repeat with the back end of the car. Start soft and go up. Go to excess and then back down. Repeat until you get a feel for the range and what to feel. You will be able to feel the back end dropping after bumps if the rebound is too high. You will also be able to look out the rear view mirror and see the chassis oscillate continuously if you're too low. It's harder to sense the back end, so learn from the front end. If you know the size of the sweet spot and how far up or down you should go from a particular cue, then you can mimic that on the back end without specifically having to feel out the motion in great detail. For example, I set my D-Spec struts to not oscillate and go just high enough to stop that motion to where I visually can't see any extra movement both line of sight off the hood and via the rear view mirror out the back window. With the D-Spec I can't go much higher till I start getting contact issues with the road, so the sweet spot is narrow. I can use the rear view mirror and set just high enough to see that oscillation stop, and I know I'm where I want to be, even if I can't really feel the back end well. Again, the Koni damping is a little different, so you will need to find visual or feeling cues that work for you. The AGX and D-Spec don't have high low speed damping, so they are more sensitive to being slightly under damped. I would expect the Koni to be a little more forgiving and likely have a broader range that still works well. That's just a personal guess though.
Experience is the best teacher. Just tweak the struts, repeat, and repeat again. You will quickly learn the breadth of influence, how it affects the car, and what feels and operates the best.