for curves, its kind of like making 4+ point sliders, the curve needs to be balanced throughout or it can look off if not done intentionally. another way to think of it is that the curve turns the same amount from each object, or across the entire slider.
easy way to have consistent curved streams is to make 3 point sliders or simple waves then use ctrl+f to convert the highlighted slider to a stream, that way you get balanced curves. copy paste the same slider and rotate it around to have all stream sections be similar.
straight streams is as simple as making sure the stream is actually perfectly straight - 2 point sliders and ctrl+f make that easier.
for streams that change distance snap, use sliders as temporary stencils if you feel you can't eyeball the curve well enough.