[exim] How to use save with Maildir and IMAP folder prefix?

So I have ~/Maildir

and under that is cur/new folders which correspond to the main Inbox

I'm trying to use save from .forward to save to other folders under ~/
Maildir

drwxrwx---   5 elastica  mail         512 Apr  6  
21:59 .INBOX.intray.known

is typical of what a folder looks like

so

should

save Maildir/.INBOX.cron/

save to a folder that IMAP folder prefix will see?