One thing my colleagues and I do is expressly offer up a starting point when reviewing changes: "the meat of the change is in xxx.go; the rest is ancillary/supporting". This allows the reader to contextualize themselves more quickly in the change, and understand the rest of the changes with greater ease.

You could take an adversarial view of it: maybe it's better if people get dropped into the changes so they're left to workout if the changes in each file stand alone rather, decontextualized from their original change.