Here are two questions that may insult your intelligence, but that's not my intent (I've had several DOH! moments when a buddy asked me similar things.)

1. Is there a divider between the top-loading compartment and the sleeping bag access compartment? If so, taking it loose to convert to a single compartment pack might give you more usable room. (I haven't seen the new Atmos 50's; the old ones didn't have this.)

2. Are you using the exterior zippered pockets on the back of the pack to best advantage? I used to keep my whole tent, including the poles, in those pockets when I used an Atmos 50; I now sometimes put my tent in the similar zippered side pockets on the Kestrel 48 I'm using now.