Yep a small changes is one computer screen of diff (36 to 48 lines) excluding generated changes (lock files, formatted files,…)

It can be even more lines as long as the hunks are continuous. Once you lose the context of change and have to “zoom out” to see where it fits in, the review time grows significantly.

A thousand characters, perhaps, and we can gently exclude whitespace in languages insensitive to it.