I concur with everyone else in thinking your pack is a bit small. Middle of the belt should be situated over your hips/iliac crest/belly button area and load lifters should be at a 45 degree angle to optimally position everything. With having a longer torso and a relatively slim waist, (if you're able to return your Mammut) I'd go with a medium size pack that features an adjustable torso. In the size you're looking at, some packs that may be worth considering that have these criteria are any of the Osprey Aethers or Kestrels, the REI Crestrail 48, or the Deuter ACT Lite series. I'd be happy to help you fit your pack if you run into problems or questions (I've been doing this for a few years as part of my job).