"The frame does not have to attach to the belt as long as the belt is stiff enough. I am going to take a wild guess and figure that ULA has considered this."
I dunno, David. Take a look at the pictures, above. The hipbelt wings are canted inward, suggesting the hipbelt material behind them that slides thru the slot in the pack body is not very stiff.
"I would direct you to Mchale, where the belt does not attach to the stays but is stiff enough to provide structure through the length of the belt to the main bag where the stays then take over."
I've owned 3 McHale packs down thru the years, as well as a Circuit, and I can say with considerable confidence that the Circuit hipbelt ain't no McHale.