Always purging old backups from same client

When the server runs out of disk space, it starts purging old backups, but it seems to always perform it in the same order. As a result, the first client always “suffers” from the shortest backup history.

Is it possible to rotate between clients in some way? First purge the oldest backup from all clients, then the next oldest backup from all clients, etc, instead of targeting a single client and purging their entire history, then pass to the next client, etc?

Current logic should be that it deletes one backup from each client starting with the client with the oldest backup (for file backups). Is this with image backups by chance?

Yes, it is.

What kind of images? VHD?

Compressed VHD.