I have always packed my frameless packs with food at the bottom and light stuff on the top. I prefer the low center of gravity. I use 2 vertical stuff sacks on top of my food bag followed, with other things on top and around those to create a virtual frame. I also have a sit pad (14"x20") against my back for solid padding and a bit more frame.
If you are ok with a higher center of gravity, packing light stuff at the bottom and heavy stuff at the middle or top will transfer the weight to your hips better. If you do this, keep heavy things really close to your back. Things like tent poles can also act as a virtual frame.
Packing your pack to create a virtual frame depends heavily on what gear you carry. Just keep in mind what could be used to make a virtual frame in your kit and to be sure to compress the pack well to avoid sagging.