Read Joshua 8:13 Using Other Translations
And when they had set the people, even all the host that was on the north of the city, and their liers in wait on the west of the city, Joshua went that night into the midst of the valley.
So they stationed the forces, the main encampment that was north of the city and its rear guard west of the city. But Joshua spent that night in the valley.
So they stationed the main army north of the town and the ambush west of the town. Joshua himself spent that night in the valley.