I have always been under the impression that it worked like this:

1. Deliveries are calculated based on the total cred gained from pwning a forum (hence, higher level forums generally reward you with better deliveries), and have absolutely nothing to do with fans.

2. There is a delivery cap of ~600k flezz for each unique forum you pwn each day (streaks are not relevant).

3. Your Charisma and Luck at roll-over work as modifiers with the amount of cred earned per forum to raise the final delivery total (only up to the aforementioned cap, of course).

Thus, higher values of Charisma and Luck are more useful when you pwn low-level forums which do not give you much cred. The same levels of Charisma and Luck are less useful on high-level forums which give enough cred to result in near-max delivery values even before stat modification.