The river flow operation needs to have contiguous rivers to figure out the flow. Try another Basin Fill operation after incise flow and before river flow to see if that makes any difference.

Once upon a time, there was only a single blur operation in there. Variable blur, however, resulted in some ugly pitting if used directly on the raw flow pattern (I need to put some more effort into that algorithm). The pre blur allows a blur to get rid of some of the noise before dong the variable, and the post blur is for cleanup n the variable blur. If you leave variable blur and post blur at 0 (using only the pre blur), then you get a single uniform blur across the surface. These blurs have nothing to do with the morphology of the system, except in a very oblique way as provided by the variable blur.