They needed to make an outpost. At the same time, they needed a place to act as the logistics base of the army. Hence, the first goal of the army was the grade 3 counties.
The target of the north troops was the grade 3 County, Hengshan County. It laid on the north-west side of Leizhou. The target of the middle troops was Leishan County, which sat in the middle of Leizhou. The south troops target was Hai An County, which stood at the southmost point.
With that, out of the five grade 3 counties, three were removed. They had taken out the hard bones of Leizhou.
Most importantly, these three counties were located at the border of Leizhou. After the army landed, they did not need to make any detours. They could just launch their attack. If not, Baiqi would have rather chosen to attack a grade 2 county.
A lone army behind enemy lines was what a military strategist worried the most about.
As the plan was set, the troops set out.