Enemies packs and zoning...

Hey Abyss...(or anyone else) do you also know how works randomization
among 4 consecutive packs, bounded from the flag? i mean, it happens
something like one battle from pack 1, then pack 2, 3, 4 and then
returns to 1... or there's literally a choice among 16 battles?

No, the pack it chooses is very random... for that reason, it has been a headache for people who speedrun the game. Even though they can predict encounters everywhere else in the game, they can't predict encounters on the Floating Continent because of this mechanic.

However... you can predict when a rare encounter will occur on the floating continent. So you can know, "the next encounter won't be a Dragon" and "the next encounter might be a Dragon", but you can't know "the next encounter will be a Dragon".