Heroes of Might and Magic V [Game Discussion]

Can someone explain how the initial monster deployment order works in battle? ...
I understand that creature initiative plays a role, but I've often encountered various combinations... for example, when attacking the same army, different deployment arrangements result in different turn orders... and sometimes even the opponent's turn order changes...
Or, for instance, how can it be explained that a monster with an initiative of 10 sometimes goes before a monster with an initiative of 12?