The logical approach would be to assign elites to the first zones, then everyone else to the subsequent zones. (e.g. GS/1K in Zone 1, 1P in zone 2, etc...)

The problem is UACO wants to sell early boarding and offer it as an incentive for credit card holders. The optics don't work as well when those folks see a 3 or 4 printed on their boarding pass, even if they are still boarding in the same sequence.