That doesn't sound like the best ratio to me, but I don't know what you are running or how good your deploy process is at catching issues. With a 4 person team, you are probably better off discussing risky/bigger changes as a whole team, and allowing 1 review for smaller, less risky changes with well defined rollback processes.

Also with a team so small you can't afford wasting it on meetings.

You might need focus, i.e. non-meeting days, 3 days a week.

I work on similar sized teams, I introduce my PRs as stacked so they are extremely consumeable in very small bite-sized code changes and build on the last one reviewed.

Do you use any special tools for this? I've heard of people "stacking" diffs in this way, but it seems like it would be clunky to review on GitHub.

This is one of the features of (yes), Meta's sapling VCS. https://sapling-scm.com/docs/introduction/getting-started/

If you work directly in the source repository that works actually really well on Github (if everybody works on its own fork instead, you're unfortunately out of luck). When opening a pull request, you just select the branch the pull request should be based on to be the previous branch in your stack. If one of those pull requests gets merged, Github will automatically rebase the stacked on onto the base branch. This way every pull requests contains exactly the changes you want it to contain, while you're still being able to stack changes by opening multiple pull requests, with each one being based on the branch of the previous one.

I use https://www.git-town.com/nested-feature-branches.html.

So every change needs to be seen by 3 out of 5 people (assuming the lead also does code review)? That sounds a bit inefficient.