It's not necessarily the size of the sidepods that counts, but the shape of the sidepods, as well as the size and shape of the inlet and outlet ducts. It's one of the more difficult areas of a formula car to design, but if done right it yields very large gains.
I'm sure that the Citation does not have "tunnels" through the sidepods, i.e. clear paths that don't pass through a heat exchanger, as that would be a clear violation of the rules. I haven't seen Brandon's car in person, though.
Remember that Road America is Coello's home track, and that he's won many races there (including, it sounds like, this one!). I'm not sure how many times Brandon has been to Road America, but I'm assuming both the driver and car took a little longer to get used to the track.
At this level it's very difficult to determine which chassis or package is fastest, since there is a lot of variability in driver and crew skill and experience. However, I think we can say with some certainty that the Citation Brandon and his crew has developed is a faster car at Road America than his competitors. Anyone disagree?
Nathan