Sorry for the delay in responding. I believe I understand your question. The zippered compartment is sewn to the rest of the pack, there is no gap between it and the main part of the pack. The straps that you see can be taken in or let out but only to help keep things from bouncing around inside the pockets.
This is a really solidly built pack, I have used it daily for a year, no wear issues. It does not have as much practical room inside as I thought it would. My old pack (similar advertised size from Lowe Alpine) seemed to have more usable space for XC ski boots, stuff like that.
IMO the only way you'd be able to store a snowboard helmet connected to the Gregory Muir 24 pack is to strap it to the outside. There are 4 loops that could be used. I have done that with my bike helmet numerous times.
thank you joseph for taking the time to give such a thoughtful response. looks like im going to have to pass on this pack as ive seen others that do have what is basically a flap on the back that can be cinched up in order to trap an item such as a helmet.
thanks again, michael