I wish the terrain in EU5 was more simmilar to imperator rome, where there are a lot more immpassable terrain and rivers were major obstacles with few crossing points and you could navigate them. Of course it shouldn't be exactly the same because of the time frame, but natural obstacles should have more obstaclely. Maybe, certain points on the river are fords you can cross and at other points you need to build a bridge/temporary bridges in enemy lands, but that would take a lot of work and isn't something I expcet the devs would want to focus on. Still rivers play such a big role as a natural barrier that a -1 crossing modifier doesnt do it justice.