I'm not sure if I understand Proxy User requirements for net folders

Documentation says the proxy user is only needed for access of users who
have no native access. Does that mean if I have a problem that a user with
native rights does not have these rights in Filr, I don't have to take the
proxy user into consideration?

Documentation also says, the proxy user should have supervisor rights on the
(root of the) target volumes. Is that mandatory? From a security point of
view I'd prefer to give these rights only to those folders that should be
visible in Filr.

My current problem is:

Netfolder: \\server\volume\folder1\folder2

User has NSS write rights on folder1. No IRF on folder2-
Proxy User has rights on folder2.

User can access folder2 with Filr, but can't write files.

Does the Proxy User play any role in this situation?