The switch from a 110mm stem to a 90mm stem has had no noticeable effect on my steering. But that may just be because the steering with the rack had become so insensitive that the effect the stem length has is negligible in comparison.
Also, to my utter embarrassment, it was only today that I discovered that the reason I had so much trouble centering my brake was because my wheel was not centered. It’s slightly off to the left. Looking at the spacers on either side of it it’s not obvious why it should be so, but I’ll flip it before the next ride to see if it’s better. And then I’ll have to recenter the bloody brake again.