I am not familiar with the details of how CFC works so I can't say for sure if anything else is needed or not. There are clearly multiple business rules built into the system considering CFC is offered only 12 hours before departure while E inventory is made available long before that. That's a trivial thing to point out but it underscores that the system could take more into consideration than whether E is available.

The elephant in the room is that FTers could be disappointed if they assume ExpertFlyer will help them predict with certainty whether CFC will be available based upon E availability. As I pointed out above, it may be a clever way to detect the possibility but I personally wouldn't take it as a guarantee.