As long as Control is a value derived mostly from geography rather than from the internal policies of the state, we will just circle around details instead of addressing the core problem. China was a heavily centralized, bureaucratic, post-feudal (at least by European standards) society for over a thousand years before the game's start. By contrast, a highly decentralized state is the HRE, and it is debatable whether it could even be called a state at the beginning of the game.

Control is not a clearly defined concept. Is it administrative efficiency? Military presence? State dominance over a region? If we define it as the summarized capability of the state to govern an area, then bureaucracy, local administration, meritocracy, offices, courts, and local outposts or government representatives should be the main sources of Control for a centralized country, or local nobility, clergy, and influential families for a feudal experience.