Not all PPO networks are the same in size or contract; the insurance company is separate but can be part of the same company. The network dept/company’s responsibility is to maintain or negotiate a deal with every medical facility, doctor on each medical code. The bigger/better the network, the better the contracted price. Here is an example:

Right ankle x-ray
PPO-A network; facility price $350 – contract $175 – Insurance $75 – Client cost $100
PPO-B network; facility price $350 – contract $235 – Insurance $75 – Client cost $40

As you see, PPO-B is a more extensive and better negotiated medical network.