China may give priority to sensor protection of naval bases and then seas in the following order: Bohai Sea, Yellow Sea, East China Sea and then South China Sea. Proximity of seas to Beijing may be one criterion. Officials and politicians in Beijing would be concerned about sub launched missile range to Beijing - this includes SSK launched cruise missiles. Also the smaller the sea (smaller in the north) the faster that sea can be "sown" with sensors by Chinese forces.
"China’s Undersea Trip-Wire
The seabed-based component of this network comprises arrays of hydrophones and magnetic anomaly detectors spaced along undersea cables laid at the axis of deep sound-channels roughly [“normal” orientated] to the direction that the arrays are to listen. This capability is next paired with maritime reconnaissance/ASW aircraft assets to establish a multi-tier ASW network. The first naval bases to be covered by this network were the PLAN’s submarine bases in four sites: