‘ And all the people, the people of war who were with him, went up, and drew near, and came before the city, and pitched on the north side of Ai. Now there was a valley between him and Ai.'
The army made the ascent and camped to the north of Ai with a valley between them and Ai. Notice the stress on the slow approach - ‘went up, drew near, came before, pitched on the north side'. They were feeling the effects of the climb. Some commentators would have him attack at once, but he wisely rested his men. But he did it within sight of the city so that they would realise what was happening and anticipate a frontal assault.
It was at this time that he was able to survey Bethel which made him set a further five eleph men in ambush. He wanted to protect all sides.