An editorial fit question about balancing stability with freedom to move.
1 answer
Aim for secure and comfortable. A backpack that swings away from you needs adjustment, but pulling every strap as hard as possible is not the solution.
Different straps have different jobs. REI’s fitting guidance warns against overtightening the hipbelt, load lifters and sternum strap. The sternum strap should help position the shoulder straps while leaving your arms free to move; it should not feel like a band squeezing your chest. Thule separately explains that compression straps can bring the packed contents closer to your back.
Try a small change, then walk around before changing something else. For example, if the contents shift but the shoulder harness feels comfortable, look at the internal load and compression rather than immediately shortening the shoulder straps. If a strap edge digs in, more tension may make that particular problem worse.
Make the comparison with the belongings you actually carry. An empty backpack can feel acceptable in several positions and behave differently once a laptop or clothing cubes are inside. The setting you want is the one that controls that real load without making you keep shrugging, tugging or restricting ordinary movement.