However, I don't think we really know where satiety comes from yet, that's why we have all of this research on the topic still. There are a few different theories, but I wouldn't call them proven.

It may not be a sensation related to some measure of the volume of matter in your gut. I think it's also related to gut microfauna such as lactobacilla, and appetite is definitely related to the brain as well through the gut, so it probably gets pretty complicated and possibly is very individualized. I'm no expert, but I do read a lot about these topics.