Out of all the frames we sell to customers, less than 1% need aluminum frame/custom bended stays. Some will need to go from a standard back composite to a flat back, but again, very few need something different.
Patrick and I have talked about the flat vs composite in great length since I met him a few years ago (my back is flatter than plywood) and here's what we've come up with.
The flat back composite will work pretty dang good on curved back users, but a curved back will not work on a flat back guy. This means the curved back guy that's using a flat back stay will not get the crazy pressure in his back that happens when this is reversed.
Now when someone like me uses a standard stay, I WILL get some pressure when packing a heavy load that can cause pain. This is because the bend for standard back does not distribute the weight to the entire lumbar pad. What I actually feel is the majority of the pressure on the upper part of the lumbar pad. If you take someone that has a big curve in the lumbar region and they use a flat back stay, the pressure is distributed throughout the lumbar pad, but it won't keep the weight on your hips as well as the curved would.
Keep in mind that none of this is 100% exact all the time, but no matter what your situation, we can get the pack to fit you.
The options that Kifaru offers is why I feel we can fit just about anyone. Let's say I get a call from someone that says they don't like the curved stay in their frame...no problem, as we will just put a straight aluminum stay in the frame. We have never done this, but we can if needed.
If someone wanted a HUGE bend in the lumbar region, but didn't want a huge lumbar pad, then we can do that as well.
Long story short, we can get just about anything figured out and fitted if you give us a chance to do so.