I found FV as a profile to be wholly underwhelming. It's no better than just running fdesetup to enable deferred mode for the current user. It has no additional intelligence and is just as likely to fail, especially if it targets the wrong user.
What does an "fdesetup status" return?
Thanks for the response alex,
Do you recommend enforcing FileVault2 through a policy instead then?
fdesetup status on the Mac in question returns:
FileVault is off.
Deferred enablement appears to be active.
Sound like the OS is waiting for you to enable it, usually at log out you will see the pop ups to enable/start the encryption...
C
That said I use the policy as I want to set FV at log in...
This is how we have FileVault enforced in our environment:
1. We create a Smart Group, labeled "FileVault = No"
Criteria:

2. A policy is created to enable FileVault on a machine:
- Scoped out to Smart Group FileVault = No
- Triggered at recurring check-in, Once every day

When a computer meets the Criteria of "FileVault = No" a computer is moved into that Smart Group and the Policy is triggered up to (1) times that day.
Hopefully this helps you!