How to Implement Retention Policies with rdiff-backup?

I’m currently using rdiff-backup on a Debian system to perform daily backups via a cron job like so:

rdiff-backup /var/www/html/ /backup/rdiff/html/

However, this approach is generating a large number of backup files. Previously, when I was using rsnapshot, I had different retention intervals configured as follows:

rsnapshot.conf:

retain  alpha   6
retain  beta    7
retain  gamma   4
retain  delta   3

And the cron job:

0   */4 *   *   *   /usr/bin/rsnapshot alpha
50  23  *   *   *   /usr/bin/rsnapshot beta
40  23  *   *   7   /usr/bin/rsnapshot gamma
30  23  1   *   *   /usr/bin/rsnapshot delta

How can I implement a similar backup strategy with rdiff-backup, where I have fewer and fewer backups as I go back in time? Specifically, I’d like to keep daily backups for a week, weekly backups for a month, and so on.

I’m aware of the --remove-older-than option in rdiff-backup, but it doesn’t quite meet my needs. Using –remove-older-than would remove all backups older than a certain point, which isn’t what I’m looking for. I’d like to implement a more nuanced retention policy similar to what I had with rsnapshot.