I believe that there is a genuine physiological effect that makes it a good idea to have the area of code that you need to think about fit entirely on one screen, without scrolling. There is probably an upper limit to the screen height where that limit is useful: I would believe a 100-line function to be above it and a 24-line function to be safely below it, but I wouldn't want to hazard a guess in the middle.

It's all to do with how your brain processes what it's seeing, and the planning processes involved in getting to the next bit of information it needs. If that information is off-screen, then the mechanisms for stashing the current state and planning to move your hands in whatever way necessary to bring it onscreen will kick in, and that's a sort of disfluency.

Similarly with tokens too far from whatever you're currently focused on. There's likely to be a region (or possibly a number of tokens) around your current focal point within which your brain can accurately task your eyes to scan, and outside that, there's a seeking disfluency.

I think this is why you get weird edge cases like k and j, where they pride themselves on having All The Code in one 80x24 buffer, and it actually works for them despite breaking all the rules about code legibility.