Trade route and religion spread range is not a fixed number of tiles as in vanilla. Here the range is 12 movement points by the shortest path the pathfinder can find. In other words, pick a warrior inside your city without movement promotions and see if you can reach destination within 6 turns (the pathfinder shows how many turns you need to reach every tile). Crossing hills, forests and jungles, tundra and desert, rivers, and lake and mountain detours, all this is taken into account. Remember that land trade routes cannot embark. So to extend range the simplest thing to do is to build roads towards the target. Moving from one tile with a road to another will consume 2/3 movement points and remove terrain movement penalty in the second road, but for rivers which require the bridge feature from Construction technology. Prior to bridges, it may be faster to make a detour than crossing short rivers. Side note: the warrior can move up to three tiles using roads. By this logic, building railroads also help, but I can't remember what the speed is. Other ways to increase range, but you already know, come from buildings like caravansary, trade technologies and policies. And for religious spreading, their national wonder and enhanced traits do the trick. I need to confirm this: Enemy units zone of control affects range at the moment to establish a trade route. And this: Civ UAs that grant movement bonus also affects trade range, i.e. the trader benefits from UA.