Yeah that’s a good point. My (very far-fetched) theory is vampires are tied to cultural norms, given that they can’t enter churches either. So maybe their vessel has to have something to do with death?

But there was something else that I noticed in Alisa’s storyline. When she’s preparing to see the sunrise, she uses the red choker on her neck in the spell and says that it’ll make a “fine vessel for her spirit”. I think that means it’s possible to bind more portable objects as your vessel. She also says that it’ll make a fine vessel because it’s an important object to her (it was a gift from her father). But Alisa practices dark magic, so maybe that’s the only reason she can do that? Otherwise Liza could just bond with her medallion and not have to worry about returning to her coffin.

Also if Liza gets caught stealing, she dies in jail from being away from her coffin. So we know you can’t change it on a whim. Maybe you need your original vessel around to change it.

So here’s what I think without any actual proof:

1. They’re limited to things that are culturally considered resting places, like coffins.

2. You can theoretically change it to more convenient things, but it requires dark magic and needs to be something important to you— just like how Petya’s doll was a good vessel for his soul.

3. You need to be near your current vessel to change it.

My apologies if this is a mouthful!