The tacocat issue was solved in private a long time ago, his biome simple did not have space for long rivers, so the river would start and immediately end for lacking space to extend.
The map border (that variable you tried editing) is just the area outside of the visible map portion, I use its size with that variable to avoid generating stuff like rivers outside of the playable area.
The actual world size is not as easy to change, because it is interconnected with a bunch of other stuff.
Now, the issue that a normal map is too small for you, have you filled a normal map yet? How about at least just 10% of it? (I will guess not, but if you did, please show the world, it would be amazing)