Vincent Baker is clear about the purpose of Fronts, so we don't need to guess or speculate. The AW rulebook says (p 136):
A front has some apparently mechanical components, but it’s fundamentally conceptual, not mechanical. The purpose of your prep is to give you interesting things to say.
He goes on:
As MC you’re going to be playing your fronts, playing your threats, but that doesn’t mean anything mechanical. It means saying what they do. It means offering opportunities to the players to have their characters do interesting things, and it means responding in interesting ways to what the players have their characters do.
He also says the following (pp 109, 136):
ALWAYS SAY
• What the principles demand (as follow).
• What the rules demand.
• What your prep demands.
• What honesty demands. . . .
Creating a front means making decisions about backstory and about NPC motivations. Real decisions, binding ones, that call for creativity, attention and care. You do it outside of play, between sessions, so that you have the time and space to think.
Preparation of fronts doesn't
change how any move is resolved (though it may introduce a custom move, which typically will be in lieu of what would otherwise be a GM soft move, or perhaps the more generic Acting Under Fire). It certainly doesn't
dictate how any move is resolved. It does bind the GM, by reference to prep, as to what interesting things ("badness", "spots" and "opportunities", in the AW parlance) the GM introduces into the fiction.
Within the framework of Apocalypse World, it doesn't make any sense to worry about whether there were
really 10 or 12 or 15 opponents in the encounter. A front in AW is simply not this sort of prep.