Right, and how is that differentiation between Zones 4 & 5 determined in KLM's case? It's not just randomly assigned, right? How can I get in Zone 4?

For example I know United will board Economy back-to-front, so if I have the option to pick a seat I will pick it toward the rear so that I am in a group that will board earlier (which I believe is usually group 4 vs. group 5 in United's case). Or I've heard some other airlines will board the window seats first, but I've never actually seen that.