sleeping pad-pack frame

I just use a section of a z-rest pad..4 folds worth..to stiffen up the back a bit. The Circuit does have the suspension hoop so I don’t think I need too much support from the pad. The rest of my z rest is carried outside the pack and used as my sit pad for breaks etc. This setup is working well for me.

You have identified the great divide in frameless packs, rollers v. folders. The former roll the pad into a cylinder, insert it into the pack, expand it firmly and pack everything inside the space thus created. What you get is a load closer to the back, protection of the gear, less back padding. Folders experience the very problem you noticed. Check with the manufacturer for their recommendation, but do what works for you anyway.