I think you've mentioned exactly what the bag is designed for and that is on the bike, your back is curved, and the padded sections at the back sit on your back while the middle lets the air flow, but off the bike it has a huge gap in the middle - the Infinity does the same thing although it's harness system is a bit different:
The rigidity of the bag at the back, whatever they use to reinforce it seems to make it that way, great on the bike, not so good off the bike.
I think you've mentioned exactly what the bag is designed for and that is on the bike, your back is curved, and the padded sections at the back sit on your back while the middle lets the air flow, but off the bike it has a huge gap in the middle - the Infinity does the same thing although it's harness system is a bit different:
The rigidity of the bag at the back, whatever they use to reinforce it seems to make it that way, great on the bike, not so good off the bike.