Another thought....how far in are you dunking your sponge cloth thing?

I used a rectangular one, and only dipped mostly the corner, maybe 1/2" -3/4" into the dye. Could it be you have too much product on the sponge and that's why there's streaks being left??

I feathered and feathered with this thing, mostly with out re-dipping.
You can tell which "corner" I used mainly and can tell I laid it a little flatter when I did the feathering..that's how the rest of the cloth got black. It was this technique that smoothed out/blended/evened out the streaks.