How does blood loss work exactly?

Is there a limit to how much blood loss can be tracked/stored? Nothing about it's description implies that, but I'm noticing that the blood loss meter grows very quickly when I first start attacking a monster/boss, then stops growing entirely, or grows much more slowly. The way I understand it, it should be continually growing as long as the monster is bleeding, and so I imagine if the first 10 seconds of a boss fight results in x blood loss, then I can expect to see ~2x blood loss after 20 seconds, but this does not seem to be the case and the bar very clearly is not twice as long. What am I missing? Another note, after looking more closely at the blood loss meter, I see that it starts out with a sort of gap in the middle, that shrinks as the meters grows, and it's when that gap has fully filled in that the meter fails to continue to grow. Thanks for any help!