1. Question: What pad are you using to pad your back?
A full length Ridge-Rest would be TOO much (too thick), a RED tosro-light inflatable would be just about right (folded once, not to thick).
If it's TOO thick, the mass of the weight will be too far from your spine, and it'll be tippy and awkward.
If you do have a closed-cel-foam pad, just fold it once, or make a "tube" and slide that in your pack.
(you note "short ridge rest" in your posting, just fold it once, or make a tube)
2. Use the side compression straps to snug the load so the loaded pack isn't "droopy" … This pack is surprisingly big for a light pack, and if the load isn't snug and slightly compacted, it'll sag down and feel uncomfortable.
3. Inside the pack is a sleeve (held closed with velcro) and inside is a small sheet of foam. Is it the white foam? If so, it's kinda crappy. Pull it out an replace it with a stiffer foam, like the blue enslolite foam. That's what I did with an older model.
If you plan on a heavy load, like a 3 week unsupported trip, take a sheet of brown card-board, cut it to fit in the sleeve, and add it to the sleeve. Paint it with acrylic paint for waterproofness. This helps a little bit (worth the extra weight)
Or, find a sheet of thin (light, stiff plastic) I found some stuff at my hardware store that would be perfect. Search your garage, there is LOTS of plastic (that we treat as trash) that works perfectly.
4. The load lifters help a tiny bit, don't expect anything magical. Loosen them completely, then put the fully loaded back on your back, then – adjust your shoulder straps to a nice place – then gently snug them to a place where they begin to pull the pack toward your shoulder then stop.
