Those are like the RLs I had. The forward lean is "integrated" with rotating the highback. Meaning you get a little of each but you have to make a compromise. It is those screws on the side that usually are used "just" for rotating the highback, now as you move the highback forward or backwards you can see the angle in the forward lean change.
It's kind of a compromise but it keeps them light and quite frankly you don't need to rotate those highbacks they are flexy.