I had a discussion with Lee Larkin that bears on this. The conditions that people were/are hunting in varies widely by area. Out here in western Washington, we have serious underbrush. If you're not on a trail you're working hard to get through it. I use a flap on my hunting pouch. If you're in an area where there isn't much brush or better yet, no brush(like eastern Washington) then there isn't as much reason to have that flap to secure and keep everything contained in the bag. If you're shooting at a range or on a trailwalk you really don't need a flap at all. I believe that conditions drove the design of the bag, how it hung on the person, and how the horn was attached or carried.
Oh yes, Really nice outfit Tim.
Steve