Hopefully someone with experience at pack fitting for more traditional packing weights will respond.

I hope no one minds a related comment about pack weight, however: as I've lightened my load I've found that various pack fitting issues and related special pack features (load lifters, etc) are just decreasingly important.

For a more casual, infrequent backpacker, getting a more traditional backpack and doing a one-time fitting might make perfect sense. It's certainly a lot of effort and possibly expense to lighten up enough to really make a difference, but it's nevertheless an alternate approach to keep in mind.