The general intent behind a funnel is that it’s for items that we haven’t really considered properly yet. Remember that even if you have a backlog in Kanban, the backlog is not necessarily ordered. So, this whole notion of sequencing a backlog is more a thing for Scrum than Kanban. It’s not something that we necessarily do in Kanban.
In my opinion, the section on the definition of workflow in the Kanban Guide is probably the most important section. If you don’t understand your definition of workflow, many other things don’t work that well in the Kanban Guide as a result. If you don’t get that part, it’ll be difficult to really make progress.