Shorter legs affect saddle height, not setback. Saddle setback depends mostly on your body weight distribution and your typical power output. The first - body weight distribution - is mostly about torso length, the longer - the bigger setback you'll need to be comfortable.
I was adjusting it other way round: started with KOPS, rode about a week, moved a few mm back, rode about a week. At first it results in very noticeable excessive pressure on hands (right at KOPS), then it progresses to just some numbness on long rides (i.e. 60-80 miles), then even this goes away. And if you move it even further back then there is hardly any difference in hand pressure anymore, which means that you probably just passed the optimal point and should move the saddle a bit forward. Too far back IMHO makes it more difficult to ride fast.