I'm designing my first pack (frameless, ~35 liter, shooting for 8 oz or less). Teaching on a university campus, I observe a lot of people wearing daypacks, and almost all have torso lengths much shorter than the actual torso length of the wearer. Often this means the yoke winds up somewhere near the middle of the wearer's back.
I've also measured the 25 liter pack I've been using for trips up to 4 days--sure enough, vertical distance between strap attachment at top and bottom (which is also the attachment point for web "hip belt") is only ~14".
In contrast, measuring from strap attachment to center of hip belt on my Osprey Exos (size M), the distance is 16" or a bit longer. Obviously, the point where the strap crosses the shoulder on any of these packs is higher than the attachment point on the pack bag, but it still seems like the average day pack is too short.
If I'm making my own pack, I'd like the fit as custom as I'm able to make. My torso length is 18", and I'd like my pack to have a wide-ish belt that fits at actual hip level. Thinking shoulder straps and hip belt made from pack cloth and 3D mesh--no other padding.
Any pack builders out there have suggestions for a good way to determine length from center of hipbelt/lower strap attachment point to top of strap where it attaches to pack bag?
Hope my descriptions are clear enough. I can add some photos or drawings later if not.