I have two recommendations: Make 20% draft for big PRs. The issue with big PRs is that the overall design is already committed. It's hard to tell the person to

I have two recommendations: Make 20% draft for big PRs. The issue with big PRs is that the overall design is already committed. It's hard to tell the person to redo everything according to a different design. So instead, have the author create a mock PR that outlines the desired changes, and have that being reviewed. This allows to have deeper conversations than if the code is aligned properly. The second thing is; do synchronous reviews for big PRs. Actually take the time to have a 1:1 video call and walk through the code changes. You will be surprised how effective that is, and it helps bond the team together.