Yes, I'm finding the result odd. I really did expect some sort of inverted V result where a medium sized max-width was "just right". Unfortunately, with a doubling of the sample size, the ordering remains pretty much the same: 1300px beats everyone, with 900px passing 1200px and 1100px. I'm starting to wonder if maybe there's 2 distinct populations of users - maybe desktop users with wide screens and then smartphones? Doesn't quite make sense since the phones should be setting their own width but...
A bimodal distribution wouldn't surprise me. What I don't believe is a spike in the middle of a plain. If you had chosen increments of 200, the 1300 spike would have been completely invisible!
If it's worth saying, but not worth its own post, even in Discussion, it goes here.