Is the blood point bonus based on where survivors or killers are needed or is it time based?

Like the 1.5x bonus that often shows on either of the two. In my experience it seems to be based on time but I've always assumed it was based on where they're needing more players to go to, I've been curious about it and can't find any info online as it's a somewhat difficult topic to Google and get related answers, is it confirmed anywhere or do we just have a good guess at least? I know it doesn't really matter as the bonus is minuscule but I'm new and curious lol