When fluting these frames, is the idea to get the whole part flat, which would require a lot of fluting on the short inside flange, or do you just need to align the rivet holes on the outside flange? I'm guessing the latter, because it looks like the frames create sort of a truncated pyramid (for stiffness, I'm guessing) and that to flatten them would be 1) very difficult and 2) a bad idea.