Looking at possibly getting this as a new winter/alpine rucksack. Just seeking calrification on the capacity as far as the S/M - L/XL goes as the dimensions are different but capacity remains at 40L. I'm making a guess that he S/M is a shade smallr. Also, does anyone who uses this 'sac have a problem with getting a rope under the lid or does the opening mean it can only go over the lid? Hopefully I'd manage to get everything inside. They seem to be quite scarce at the moment, particularly the BigSur Blue version - I'm wondering if new versions are due soon.