A little FYI history. TiGoat no longer produces the Raven xl, it morphed into the Raven Omni. The xl was simply a longer version of the Ptarmigan for tall folks. It had the same foot dimensions as the Ptarmigan, so it tended to curl wide full length pads if they were used inside the bivy.
The Raven Omni has a wider foot so it will accommodate long thick pads and heavy winter bags. The unique Omni zip was developed for two reasons... versatility and production. It works as either a chest, L side zip, or R side zip... some folks have more than one sleeping bag and the zipper isn't always on the same side. From a production (inventory) point of view, one bivy covers 3 options... less time and less money. We can keep them on the shelf... faster turnaround time for the customer.
Hope that helps,