One of my 'issues' when people consider BIAB is the lack of acknowledgement that the bag is in fact your mash tun. While it is true that the original Australian method was a full volume mashing, it has evolved beyond that initial process definition to become an extremely flexible and economical replacement for the traditional mash tun and filter screen. Even at full volume, it is no different from a standard single infusion process. I've even done a step mash using a bag, ending up at full volume at final mash temperature.