Rule of 6 - The center node in a full cluster of 6 will be either 1) empty or 2) contain a defensive subsystem. If it contains a subsystem than the system core is one of the six surrounding nodes.

(Far) Corner Tendency - The corners of the hack contain white nodes. By the nature of the maze, the far one has a higher liklihood of containing the system core.

Rule of 8 - "Before 8 it is bait". The system core is always at least 8 grid spaces away from the starting point. If no such space exists, the system core could be anywhere.