The source templates used for books to not allow you to specify Repositories. The theory behind this is that a book can be located in many places. I don’t agree with this theory. When I look at the source I want to know where I saw it in case I want to look at it again.
If you don’t specify a template you can use the repository field.
When you use "Online Publication (Image Copy by Title)" you can use the Website Title (Open Books) and URL fields to identify where you found it.