An editorial explanation of bag position for daypacks and packs with a supporting hipbelt.
1 answer
There is no single distance below your shoulders that works for every backpack. Begin with the bag’s harness design and, if it has one, the position of its load-bearing hipbelt.
For a pack designed to transfer load through a padded hipbelt, the belt belongs around the top of the hips, with the harness adjusted to match. A small daypack without that supporting system needs a different assessment: it should remain controlled against you without its contents swinging around or the straps forcing an uncomfortable posture.
The packed shape matters as well. Thule describes compression straps as a way to manage the load and draw it closer. That can help when a partly filled backpack has belongings gathered in a loose outer bulge. Compression will not shorten a back panel that is too long for your torso.
Use a side view in a mirror or a photo to understand the position, then trust the loaded trial more than the photo’s appearance. Walk, turn and reach as you normally would. If moving the bag higher fixes one problem but creates another, inspect the torso setting, strap shape and placement of rigid items instead of chasing a supposedly universal height.