There is nothing so formalized as a lore bible for BP. When coming up with the rules for subspace in WiH, we operated on a couple of basic principles:
1. Subspace travel is effectively instantaneous within a solar system. There is no strategically relevant difference between jumping from Pluto to Mercury or from the Earth to the Moon; travel times are affected, but not in a way that would allow for more than firing off an early warning.
2. Subspace travel requires a navigation solution. In order to safely jump, a ship needs to calculate a jump solution, which in turn requires a lot of very precise measurements that take time to complete. Jumping without such a solution is possible, but runs the risk of your jump trajectory intersecting with a gravity field strong enough to pull you back into realspace.
3. Subspace drives require a charge time. In order to jump, the ship's generators need to build up a charge; jumps cannot be completed on a partial charge, but nothing stops you from just strapping another jump drive to your ship. Smaller ships recharge faster than larger ones.
4. Subspace travel is both enabled and hindered by gravity interactions. While you can jump out anywhere, you can only go so deep into a gravity well - smaller ships can go deeper than larger ones. Similarly, travel far away from a star is difficult too: larger ships cannot exit subspace without a minimum level of gravity present.