Its a matter of scale really.
Combat works with basically moving assets into target zones where you can make a strike to take down the opponent.
A duel is just 2 people in a fight, so it ‘zooms in’ very closely on them. In a duel the assets are a knife and/or a shield and the zones are a personal zone and two ‘guard’ zones that protect it.
A skirmish is a group of people fighting. So here the assets are often weapons, but can be soldiers or thugs you have on your side. The zones are the different areas of the site - ‘by the steps’ or ‘near the door’ or just ‘this half of the alley’.
Having said that, in a skirmish the zones are as detailed as the GM wants them to be. If you like a lot of tactics in your combat you might divide a simple alley into four or five different zones. But you might just as easily make it one zone and fight it out without too much asset movement.