iMessage Storage on iCloud

Hi everyone just had a quick question about how iMessage is being stored on iCloud. I recently noticed some of my messages threads are taking up a lot of my iCloud storage, around 10gb across a few threads. I decided to delete all those top conversations and have reduced my total conversations size to 1.7gb, however when I look at what's being backed up to my iCloud, it's still showing the original 10gb being backed before I deleted my top conversations. I was under the assumption like how photos are backed up, that once you delete the content from your phone or other devices, it's deleted on the iCloud backup as well. How can I reduce my actual iMessage backup size? I would like to have those 10 gigs freed up, I'd rather not disable iMessage on iCloud and wait 30 days for it to be deleted.