Ah I see, I think... Yeah the river width calculation does work something like that(it goes a bit crazy when the river gets quite long).

When I look at real terrain, it's like the highest areas have the most relative height differences where they've been eroded ,big chunks taken out of mountain areas, less erosion on a bigger area at low elevations, and I'm finding it hard to balance this with the erosion systems because the lower areas are more likely to be passed through more times by longer rivers...it kind of gets the amount of power from the exponent of the height, then gets less(???) as it goes downhill and grows in size....something like that anyway.