Delta uses (or has experimented with) a tandem system on some larger planes. Imagine that zone numbers were consecutive from back to front. Then a tandem system might go 1, 4, 2, 5, 3, 6.
The aim is to have two or three areas of stowing instead of just one which in the traditional back to front system works, as you would guess, slowly from back to front.
Ideally there should be stowing all up and down the aisle but no one has figured out a system for this yet. (Not counting non-systems such as someone seated in the back putting his carry-ons up front.)