[jmnicolas]

Shouldn't it be at the bottom of the pack then ?

[masklinn]

No, the bottom of the pack is completely outside (behind) the hips. If you put it at the top of the pack, you'll naturally bend forward slightly to an equilibrium between your torso and your backpack, the top of the pack will be roughly above the hips.

[hobs]

Exactly why you see the head basket carrying in many countries that have to do long haul water carrying.