Your right, the hallway should be 4'. it sounds like air is escaping somewhere. We have the 12' set and we have to keep the fans on low so it doesnt cause to much pressure so the customers cant get out of it. You didnt say if you purchased the fans with the bags or if you are using something different that what they use. That might be the problem if it isnt the proper fans. We never had a problem with ours not filling up evenly so i would say it is the air escaping somewhere. Just my two cents!