How could one represent a composite key functional dependency of a non key column in 5NF (Fifth Normal Form)?

users
----------
id
name

events
----------
id
name

events_users
---------------------------
id
user_id
event_id
participation_type (ENUM)

5NF needs each table to be represented in its own small entity.

What is the reason having participation_type in events_users is in or not in 5NF?

What is a better solution?

I've been using the DataMapper library of CodeIgniter, where each table needs to exist independently, i.e be in 5NF.